Excerpt - Advanced Installer Study Guide

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AdvancedMobile Electronics

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AdvancedMobile Electronics

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iv THE ADVANCED INSTALLER STUDY GUIDE TABLE OF CONTENTS

TABLE OF CONTENTS

Introduction ....................................................................................................xiv

CHAPTER 1 – VEHICLE ELECTRICAL SYSTEMS

Electrical History of Vehicles ..............................................................................2Electrical System Components ..........................................................2The Electrical System Backbone ........................................................3Example of Electrical Power Supply and Demand ............................3Function of the Battery ......................................................................4Function of a Power Supply Capacitor ..............................................5Audio Signal Content Determines the Real Electrical Work..............6The Relationship of Voltage, Current and Resistance (Ohm’s Law)......................................................................7Voltage ................................................................................................7Current................................................................................................8Speaking of Ohms (Electrical Resistance) ..........................................8Multiple Resistance Values..................................................................9Resistance in Series ............................................................................9Resistance in Parallel ........................................................................10Ohm’s Law and Electrical Power (Watt’s Law) ................................11

Practical Example Using Ohm’s Law and Watt’s Law ................................................................................................12

Easy Ohm’s Law and Watt’s Law References ....................................13Batteries/Power Storage Technologies ..............................................................13

“Wet” Lead Acid Batteries ................................................................15Maintenance-Free (Sealed) Lead Acid Batteries ..............................15AGM (Absorbed Glass Mat) Batteries ..............................................15Gel Cell Sealed Batteries ..................................................................16Automotive and Deep Cycle Battery Differences..............................16Parasitic Current Drain ....................................................................17

Charging and Starting Systems ........................................................................17The Alternator ..................................................................................17The Ignition Switch ..........................................................................1912/14-Volt Electrical Systems............................................................2136/42-Volt Electrical Systems............................................................21Hybrid Vehicles ................................................................................23

OEM Anti-theft Systems ..................................................................................23Power Supply and Distribution ........................................................................24

Kirchhoff’s Voltage Law ....................................................................24Kirchhoff’s Current Law....................................................................24High End, Appropriately Chosen Cables..........................................25Fuses and Circuit Breakers ..............................................................27Power Storage Capacitors ................................................................28

Applications of Electronic Components ............................................................29Resistors ............................................................................................29Potentiometers ................................................................................30Incandescent Light Bulbs..................................................................31

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Capacitors ........................................................................................32Inductors ..........................................................................................37Relays ................................................................................................40Semiconductors ................................................................................44Diodes ..............................................................................................45Light Emitting Diodes (LEDs)..........................................................48Transistors ........................................................................................50Integrated Circuits (ICs) ..................................................................53Microprocessors ................................................................................54

Digital Fundamentals ......................................................................................54Databus / Network Communications ..............................................54Control Modules and Diagnostic System Acronyms ........................54Multiplexing......................................................................................55The Binary System ............................................................................57Integration into a Databus ................................................................59IEEE-1394 (IDB-1394) ....................................................................61MOST ................................................................................................61Optical Data Transfer ........................................................................62

Sample Test Questions ......................................................................................64

CHAPTER 2 – ADVANCED INSTALLATION KNOWLEDGE AND TECHNIQUE

Tools and Safety ..............................................................................................68Hand Tools ........................................................................................68Specialty Installation Tools ..............................................................71Power and Pneumatic Tools..............................................................74Shop Safety........................................................................................78Keeping a Clean Shop ......................................................................82

General Vehicle Disassembly ............................................................................82Use of Proper Tools ..........................................................................82Panel Fastening Techniques..............................................................83Management of Hardware ................................................................83Electrical Connectors........................................................................84

Fabrication ......................................................................................................84Fabrication Materials and Basic Techniques ....................................84Plastic Adhesives ..............................................................................92Working with Plastics and Adhesives ..............................................94Working with Body Fillers to Cosmetically Finish Projects ............95Types of Body Filler and Finishing Materials ..................................95Smoothing Shapes with Body Fillers ................................................96Finishing Projects with High Build Spray Primers ..........................97Painting with Plastic Textures and Colors........................................99

Electronic Testing and Test Equipment ............................................................100Circuit Verification..........................................................................100Testing Wires in a Vehicle ..............................................................103Taking DC Voltage Measurements..................................................104Taking AC Voltage Measurements ..................................................105Taking Resistance Measurements ..................................................106Checking Continuity ......................................................................107Taking Standby Current Draw Measurements................................108

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Battery and Charging System Testing ............................................109Testing Voltage Drops ....................................................................113Notes on Voltage Drop Testing Applications ..................................114Identifying and Troubleshooting Noise ..........................................115Powerline Noise ..............................................................................118Radiated Noise ................................................................................118Ground Loop Noise ........................................................................120Accessory Noise ..............................................................................121System Noise ..................................................................................121Proper In-Dash Installation ............................................................122In-Dash Installation Accessories ....................................................123

CEA Standards for Aftermarket Automotive Harnesses ..................................123Proper Speaker Mounting ..............................................................124

Basics of Aftermarket Amplifier Installation ..................................................126Getting Power at the Battery (Direct Battery Feed) ......................126Grounding ......................................................................................126Getting Signal into the Aftermarket Amplifier ..............................128Interfacing with OEM Source Units................................................129Speaker Connections to an Amplifier Channel ..............................131Connecting Speakers (or Voice Coils) in Series ............................131Connecting Speakers (or Voice Coils) in Parallel ..........................132Understanding the Function of Input Gain Adjustment................133Setting the Input Gain Correctly ....................................................134Amplifier Mounting Location ........................................................139

Sample Test Questions ....................................................................................140

CHAPTER 3 – ADVANCED MOBILE AUDIO/VIDEO SYSTEMS

Vehicle Disassembly for Audio System Installations Audio Source Formats ....................................................................................144

AM/FM Tuner..................................................................................145Cassette ..........................................................................................145Digital Satellite Radio......................................................................147HD Radio ........................................................................................148DAT - Digital Audio Tape ..............................................................148DCC - Digital Compact Cassette ....................................................148CD - Compact Disc ........................................................................148HDCD..............................................................................................149DVD-Video ......................................................................................150DVD-Audio ....................................................................................150SACD ..............................................................................................150Mini-Disc (MD) ..............................................................................151Compressed Audio Formats ..........................................................152

Mobile Audio Source Units ............................................................................153Headunit Mounting Types ..............................................................153Source Unit Audio Output Characteristics ....................................159Peripheral Source Inputs ................................................................160

Headunit Installation Considerations..............................................................162OEM Integration ............................................................................................165

Single Ended Audio Inputs/Outputs ..............................................166Balanced Audio Inputs/Outputs ....................................................167

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Differential Audio Inputs/Outputs..................................................169OEM Interface Devices ..................................................................................169

Line Output Converters..................................................................169CD/DVD Changer Adapters ............................................................170Satellite Radio Adapters ..................................................................170Turn-on Lead Generators ................................................................171Steering Wheel Control Adapters ..................................................171FM Modulators ..............................................................................172

OEM Integration Installation Considerations..................................................172Audio Signal Processing..................................................................................173

What is Signal Processing? ............................................................173Analog vs. Digital............................................................................174Active Crossovers............................................................................175Decoders for Multi-channel Audio Formats ..................................176Installation Specific Signal Processing Considerations ..................177

Mobile Audio Amplifiers ................................................................................177Mobile Audio Amplifier Circuit Topologies ..................................182Class A Amplifiers ..........................................................................182Class B Amplifiers ..........................................................................183The Class AB Hybrid Amplifier ......................................................183Class D Amplifiers (Switching Amplifiers) ....................................184

Passive Crossover Networks ..........................................................................187Other Passive Networks..................................................................188Construction of a Crossover ..........................................................189Orders of Response ........................................................................191

Speaker Types and Enclosures ........................................................................191Speaker Types..................................................................................191Subwoofer Enclosures Types ..........................................................192Enclosure Construction ..................................................................194The Ideal Subwoofer Enclosure? ....................................................197Infinite baffle Designs ....................................................................197Semi-Closed Aperiodic Designs ......................................................199Sealed Enclosure Designs................................................................200Vented Enclosure Designs ..............................................................203Bandpass Enclosure Characteristics................................................206Single Reflex Bandpass Designs ......................................................207Dual Reflex Bandpass Design..........................................................208

Sound in the Vehicle ......................................................................................210Low Frequency Transfer Function ................................................210Uninvited Noises ..........................................................................211Importance of Damping Vibrations and Resonant Panels ..............212Speed of Sound ..............................................................................212

Speaker Installation ......................................................................................212Rear Deck Locations ......................................................................214Kick Panel Locations ......................................................................215Center Speaker Locations ..............................................................215Positioning Speakers for Optimum Performance ..........................215Tips for Component Speaker Placement ........................................221Installation of Full Range Speakers and Mid-Woofers ..................221

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Installation of Tweeters ..................................................................222Digital and Multi-Channel Sound ..................................................................223

Audio Encoding Formats................................................................224Multi-Channel Audio Software Formats ......................................229Stand Alone Decoders ....................................................................230

Vehicle Disassembly for Mobile Video System Installations ......................................................................................231Mobile Video Entertainment Systems ............................................................233Video Sources ................................................................................................233

VHF/UHF TV Tuners ......................................................................233Satellite Television ..........................................................................234VHS Tapes ......................................................................................235DVD-Video ......................................................................................236Video CD ........................................................................................242Video Games Consoles ..................................................................242DC-AC Power Inverters ..................................................................243The Video Portion of a DVD-Video Disc ........................................237The Audio Portion of a DVD-Video Disc ......................................238

Video Output Formats ..................................................................................244Composite Video ............................................................................244S-Video ............................................................................................244Component Video ..........................................................................245NTSC ..............................................................................................245PAL..................................................................................................246SECAM............................................................................................248

Basic Elements of a Video System Installation ..............................................249Video Screen Types ........................................................................250AUX Inputs and Outputs................................................................252

OEM Audio Integration with a Video System Installation ..............................253Video Signal and Power Cabling ..................................................................255Video Component Mounting Considerations....................................................256Multi-Zone / Multi-Source Audio/Video Entertainment Systems ....................259

How many sources are possible or practical? ................................260How do the source and screen selections work?............................260

Troubleshooting Common Video System Installation Problems ........................261Sample Test Questions ....................................................................................264

CHAPTER 4 - SECURITY AND CONVENIENCE SYSTEMS

Introduction....................................................................................................268Vehicle Disassembly for Security and Convenience Installations ......................................................................269OEM Anti-Theft Systems ..............................................................................270

Identifying an OEM Anti-Theft System..........................................270Advanced Security Topics ................................................................................272

Range and RF Interference..............................................................272Two-way Communication ..............................................................273Inputs and Outputs of a Security System ......................................273

Identifying Vehicle Circuits ............................................................................274Identify Positive Switching ............................................................276Identify Negative Switching............................................................276

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Identify Reverse Polarity Switching................................................276Identify Multiplex or Variable Voltage Switching ..........................276Examples of applications that use the previous switching types ................................................................278Unique Interfacing Challenges ......................................................281Advanced Relay Applications ........................................................282

Security System Placement and Mounting ......................................................287Mounting Considerations for a Control Unit ................................287RF Range Concerns ........................................................................288Electromagnetic and Inductive Coupling Concerns ......................288Vibration Concerns ........................................................................289Wiring and Connections for the Control Unit ..............................289Performing the Installation (Start to Finish)..................................291

Troubleshooting Common Security System Problems ............................................................................................294Security and Convenience System Accessories ................................................295

Paging Devices ................................................................................295Window and Sunroof Automation..................................................296

Alternative Security System Applications ......................................................297Boats................................................................................................297Motorcycles and Snowmobiles........................................................297Tractors ..........................................................................................298

Remote Start Systems ....................................................................................298System Overview and Vehicle Applications....................................298Automatic and Fuel-Injected Vehicle Applications ........................299Carbureted Applications ................................................................299Manual Transmission Applications ................................................300Diesel Applications ........................................................................300

Identifying Critical Remote Starter Connections ............................................301Ignition Switch Positions and Measurements ................................301Parking Light Circuit ......................................................................303Tachometer Signal ..........................................................................304Alternator Signal (Voltage Change) ................................................305Foot Brake Switch ..........................................................................305Parking Brake Switch......................................................................305Neutral Safety Switch......................................................................306Hood Pin Switch ............................................................................306Programmable Parameters for Remote Starters ............................307

OEM Security Interface and Bypass for Remote Starters ........................................................................................308

Disarming the Factory Security System..........................................308Factory Disarm Output Wire ..........................................................308Resistor Keys (VATS, PASSkey I) ....................................................308PASSlock 1 & 2 ..............................................................................310Transponder Systems ......................................................................315OEM Anti-theft System Bypass Modules: ......................................315

Safety Considerations While Installing and Configuring a Remote Start System ..................................................................................................316

Testing the Remote Starting System................................................316Educating Customer on Responsible Use ......................................316

Troubleshooting Common Remote Starter Installation Problems ......................317Sample Test Questions ....................................................................................319

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CHAPTER 5 – IN-VEHICLE INFORMATION AND CONTROL SYSTEMS

Overview of Data ..........................................................................................322Driver Distraction Safety Concerns ................................................322How Information on the Road Works ............................................323

Bringing Outside Data into the Vehicle via Satellite ........................................324GPS Satellites ................................................................................324Limitations of GPS..........................................................................326Positioning the GPS Device or External GPS antenna ..................326Subscriber Radio Satellites ..............................................................327Proprietary Data Satellites ..............................................................327Terrestrial Repeaters........................................................................328Bringing Data into the Vehicle via Radio Frequency Networks ......................................................................328FCC Allocation ..............................................................................328NTIA ..............................................................................................329Public Access RF Subscriber Networks ..........................................329

Sending Data from the Vehicle (Two-way Communication) ............................331Products in the In-Vehicle Information Systems Category ..........331Modern Wireless Phones ................................................................331In-Vehicle Navigation and Route Guidance Systems ....................334Testing the Route Guidance System ..............................................338

Subscription Services ......................................................................................340Digital Satellite Radio ..................................................................................340

Installation Considerations of a Satellite Radio System ................340Installing Adhesive/Magnetic Roof Mount Antennas ....................341Installing Adhesive, Glass Mount Antennas ..................................342Installing Mast-type, Commercial Truck and Marine Antennas......................................................................343Mounting the Dedicated Receiver ..................................................343Mounting the RF-Modulated Control Unit ....................................344Troubleshooting a Satellite Radio Installation ................................344

Consumer Telematics Systems ........................................................................345Installation Considerations of a Subscriber Telematics System ........................................................346Stolen Vehicle Tracking Systems ....................................................347Installation Considerations of a Vehicle Locator System ..............349

Commercial Telematics Services ....................................................................349Installation Considerations of a Commercial Telematics System ..........................................................................350

CB and Other Two-Way Radios ......................................................................351Positioning the CB Antenna ..........................................................351Adjusting the Standing Wave Ratio ................................................354

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Integration and Interface with On-board Systems............................................354Airbags ............................................................................................355The “Check Engine” Light..............................................................355OnStar Equipped Vehicles ..............................................................356

Additional Resources ......................................................................................356Automotive Manuals ......................................................................356

Sample Test Questions ..................................................................................357

GLOSSARY OF TERMSGlossary of Terms ..........................................................................................360

APPENDIXAppendix ........................................................................................................390

REFERENCE MATERIALSReference Materials ........................................................................................404

INDEXIndex ..............................................................................................................408

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CHAPTER 3ADVANCED MOBILE AUDIO/VIDEO SYSTEMS

3

IMPORTANT MESSAGE FROM CEA:Due to the increasing complexity of aftermarket automotive electronics, it is more critical thanever that mobile products be installed in strict accordance with the manufacturers’ instructions.Mobile product manufacturers go to great lengths to design and test their products for safety,reliability and performance. Make sure that your customers get the most out of their mobileelectronics purchases by reading and following the installation instructions included in theproduct literature. A quality installation is your professional responsibility.

CEA’s Statement on Mobile Video:

When installing mobile video, navigation, or telematics products, you have a responsibility to ensure that these products are installed in a safe manner. Please adhere to the followingguidelines when installing video monitors in vehicles:

An LCD panel and/or video monitor may be installed in a motor vehicle and visible tothe driver if the LCD panel or video monitor is used for vehicle information, system control, rear or side observation or navigation.

If the LCD panel or video monitor is used for television reception, video or DVD play,the LCD panel or video monitor must be installed so that these features will only function when the vehicle is in “park” or when the vehicle parking brake is applied.

An LCD panel or video monitor used for television reception, video or DVD play thatoperates when the vehicle is in gear or when the parking brake is not applied must beinstalled to the rear of the driver’s seat where it will not be visible, directly or indirectly,to the operator of the motor vehicle.

The consumer electronics industry encourages a uniform approach to video in the vehicle. Inrecognition of consumer needs and safety, CEA’s Mobile Electronics Division recommends thesepractices. For more information, please visit www.digitaldriver.org.

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ADVANCED MOBILE AUDIO/VIDEO SYSTEMS

Vehicle Disassembly for Audio System InstallationsWhen an audio system installation is taking place, certain undeniable truthstranspire. The dash panel almost certainly requires removal if an aftermarketheadunit is going to be installed. More than likely, the dash panel removal iseven necessary for many OEM upgrades where the factory-supplied headunitis retained. A number of other areas require disassembly for an audio systeminstallation. You incur certain assumed liabilities when working on thoseareas of a customer’s vehicle, so be aware of the challenges that are commonto audio system installations.

Parts common for removal in audio system installations include:

Center dash panels (surrounding headunits, HVAC controls, etc.)

Center console panels and complete center consoles

Underdash panels (both driver and passenger sides)

Glove boxes (and surrounding area)

Front seats (both sides)

Middle and rear seats

Door panels (front, rear, and cargo doors)

Kick and threshold panels

“B” pillar panels (in four-door vehicles)

Rear side panels

Rear deck panels

Front and rear seat belts (typically held in with large Torx bolts)

Trunk cosmetic panels

Though it is generally not necessary to entirely remove the floor carpet to run wires in an audio system installation, correctly running the wires may necessitate seat belt and “B” pillar panel removal as well as entire seatremoval in some cases. In vehicles with a trunk or under rear seat mountedbattery, always avoid running audio cabling down the same side of the car asthe battery-to-alternator connection cable. This battery cable carries highcurrent and will almost certainly be a source for electromagnetic interference(EMI) related noise problem.

Most important in any vehicle disassembly is the final step: putting back allof the original hardware for panel attachment as it was originally assembledfrom the factory. Often the easiest way for an automotive mechanic to blamean audio component installation for an electrical problem stems from look-ing at reassembly of the vehicle interior panels. To remedy this, always usethe appropriate panel removal tools to avoid damaging any sensitive panel

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THE ADVANCED INSTALLER STUDY GUIDE CHAPTER 3ADVANCED MOBILE AUDIO/VIDEO SYSTEMS

Seat and seatbelt

anchor bolt removal is often

a necessary part of running

wires in a vehicle.

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clips and always be aware of where panels are stored while they are out ofthe vehicle. Laying a blanket or strip of carpet across a storage shelf helpsensure that the panels will not get any scratches while in your care. There isnothing worse than handing a customer the keys to the vehicle only to havehim notice the big scratch in the plastic dash panel that surrounds his newheadunit.

Some of the methods by which interior dash and trim panels are removedfor installation and/or modification are covered in Chapter 2 of this MECPStudy Guide, “Advanced Installation Knowledge and Technique.”

Audio Source FormatsAM/FM TUNERA tuner selects one of hundreds of public radio broadcast signals while it must ignore others. It must also reject electrical interference from car ignitions and Class D “switching” amplifiers as well as atmospheric condi-tions such as lightning and severe storms. The tuner must be able to select a desired signal, whose strength may be only a few millionths of a volt,while rejecting nearby, stronger signals, without adding to or subtractingfrom the source. Most car decks are designed to blend from stereo to monoas the signal strength of the station drops.

AM (Amplitude Modulation). AM is a broadcasting process in which theamplitude of a high-frequency carrier wave is modulated by the amplitudefluctuations of the lower-frequency program signal. The AM band in NorthAmerica operates between 520kHz to 1600kHz.

FM (Frequency Modulation). Developed in 1939, FM is a mono-based sys-tem in which the frequency of a high-frequency carrier wave is modulated by the amplitude fluctuations of the lower-frequency program signal. The FMband in North America operates between 87MHz and 108Mhz. FM tunerstypically operate in odd-numbered frequency steps in North America, whileother countries operate FM stations in much more crowded airspace. FM stations in the United States are staggered, such as 95.1, 95.3, 95.5, 95.7,

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CHAPTER 3 THE ADVANCED INSTALLER STUDY GUIDEADVANCED MOBILE AUDIO/VIDEO SYSTEMS

Always store panels with

the cosmetic side facing up

where no scratches will

occur. Avoid stacking panels

unless foam or other suitable

protection is placed in between

each panel.

When working on plastic,

vinyl or leather interior panels

face down, work on carpeted

benches or a similar soft

surface that will not scratch

or damage the panel.

The AM bandwidth in

North America is 520kHz-

1600kHz.

The FM bandwidth in

North America is 87MHz-

108MHz.

Figure 81. Vehicles with Integrated Dash Board Electronics Often Present Disassembly Challenges

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95.9, and then on to 96.1 Mhz. In European countries. The increments areboth odd and even numbers, and often in half-band increments. A typicalEuropean tuner would read 95.00, 95.05, 95.10, 95.15, 95.20 and so on. In the United States, the Federal Communications Commission (FCC) regulates the neighboring air space around public broadcast stations so that the broadcast signal is more defined when the tuner needs to lock in for consistent reception.

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Amplitude Modulation (AM)

Frequency Modulation (FM)

88.1 MHz - 107.9 MHz

540 KHz - 1700 KHzA

mpl

itude

(dB

)

Frequency (Hz)10Hz 100Hz 1K 10K 20K 30K 50K

0

FM

FM - <50Hz-15KHz

CD - 5Hz-20KHz

DVD-A - 5Hz-50KHz

Figure 82. AM and FM Frequency Comparison

Figure 83. Frequency Response of FM Compared to Other Formats

Both AM and FM analog tuners have limited frequency response. While the average human’s hearing is considered to be 20Hz to 20Khz, a typicalAM/FM tuner has a response no better than 40Hz to 15kHz. Often theresponse is not even as good as that. For this reason, many AM and particu-larly FM broadcasts compress the broadcast programming so that is has better low and high frequency response when processed through a car tuner.

Some headunits containing tuners feature RDS (radio data system) capabili-ties. RDS scrolls text on the front panel display to help sort broadcasts bytype (talk, sports, etc.) and provide drive-time warnings of accidents.

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Important AM/FM tuner specifications include:

Sensitivity: the ability to receive weak signals clearly. Sensitivity isnow measured in decibels per femtowatt (dBf). Lower numbers are generally better.

Selectivity: the ability to discriminate between two signals very closeto each other in frequency. This is important in major metropolitanareas. Again, lower numbers are better.

Capture ratio: the tuner’s ability to lock onto the stronger of two sig-nals on the same frequency. This occasionally happens if a tuner islocated about midway between two cities, for example. The lower thenumber, the better.

Stereo separation: The ability of an FM tuner to accurately separate a stereo broadcast’s left and right channel information. Measured indecibels (dB), higher numbers are generally better.

CASSETTEThe cassette tape is a small, enclosed reel-to-reel that uses a plastic filmcoated with magnetic particles. In the recording process, the cassette tape is drawn at a regulated speed across a recording head. The recording head is an electromagnetic device that can arrange the magnetic particles on thetape in a specific manner. The audio material being recorded controls theorder in which the magnetic particles on the tape are arranged. Once therecording head has arranged the magnetic particles on the tape, the playbackhead translates the particles back to audio. This is done by drawing the cassette tape across the playback head. The magnetic particles on the tapecause a magnetic field to form in the playback head that corresponds to thealternating current contained in the original audio source. Mobile audioheadunits with cassette capabilities feature a playback head only.

Cassette tapes have limited frequency response and playback quality whencompared to other, more modern formats. Many OEM mobile audio systemsno longer feature a cassette player in the main headunit, but may offer aslave version in a console or another dashboard opening. It is common foran OEM audio system to contain both a cassette player and another play-back form such as CD. The cassette has obvious sound quality limitationsand has a high noise floor (known as tape hiss) during playback.

By using a masking principle together with signal compression and expan-sion, the Dolby noise reduction system (Dolby NR) masks some of theinherent noise associated with cassette tape playback. Dolby NR achievesthis by boosting the low-level signal components during recording. This isfollowed by complementary attenuation during playback, using expansion.Dolby B helps reduce tape hiss up to 10 dB. Dolby C helps reduce tape hissup to 20 dB. Many OEM and aftermarket headunits in the past featured thisoption, though most modern mobile audio headunits are suited only forstandard playback.

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DIGITAL SATELLITE RADIODigital satellite radio is the latest advancement in automotive entertainment,offering consumers unprecedented sound quality, programming choice andnational coverage. Digital satellite radio works much like the digital broad-cast satellite systems (known as DBS or DSS) that are popular in homes. The digital signal from a satellite radio company is uplinked from a ground-based transmitter to several high-powered satellites that beam the signalback down to earth. Digital satellite radio subscribers can listen to thebroadcasts using special receivers and dedicated antennas. See the “In-Vehicle Information and Control Systems” chapter for additional information on digital satellite radio.

HD RADIO HD Radio technology allows digital radio signals to ride the same airwavesas analog AM/FM radio, bringing CD-like sound from any radio station tothe listening public along with integrated wireless data services such as news and entertainment. There are a host of new benefits that HD Radiotechnology provides with the upgrade to digital broadcasting:

AM digital has FM-like audio quality

FM digital will have CD-like audio quality

Static-free and crystal-clear reception

Wireless data services to include on-demand

Some aftermarket HD Radio manufacturers are using a separate tuner box,while others use a single-din headunit. Unlike aftermarket satellite radiotechnology, HD Radio only requires new receiver to hear HD Radio signals,and no new antenna or subscription fees are required.

DAT - DIGITAL AUDIO TAPE Digital audiotape (DAT) was introduced many years ago as an economicalprofessional grade digital recording format. Mobile players never reallygained momentum, primarily because of a lack of recorded software. Where mobile DAT players are popular, you usually find a musician orsomeone else within the recording industry creating that demand.

DAT tapes are much smaller than standard cassette tapes and therefore DATplayers only allow for the playback of other DAT tapes. DAT tapes are alsoconsiderably more expensive. The DAT digital recording format uses a 16-bitlinear pulse code modulation with selectable (recording) sampling rates of32, 44.1, or 48 kHz.

DCC - DIGITAL COMPACT CASSETTE Digital compact cassettes arrived around the same time as the mini-disc(MD) format. DCC was developed by Phillips of Europe and uses a 16- to18-bit compressed (PASC) format. DCC is not the same as DAT in either size or recording technology. DCC tapes are similar in size to the traditionalcassette tape and most DCC players will play both DCC tapes and standard

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Digital satellite radio

requires a paid subscription

and compatible receiver for

use in a vehicle.

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cassettes. Commercial DCC players for the car are not widely available in theUnited States. DCC headunits were available primarily in Europe in the earlyto mid-1990s.

Much like DAT and mini-disc (MD), DCC tapes that have pre-recorded titlesare difficult to find in most music stores. A user who wants to enjoy DCC inthe car will most likely have to have a DCC player/recorder in their homeaudio system to make the tapes. Because DCC was always more popular inEurope than in the United States, there was little if any evidence of this for-mat around in the mobile electronics market. These days, the recordable CDformat has all but consumed the market for DCC.

CD - COMPACT DISC The compact disc has been around since 1982 and CD players for the auto-motive environment since 1984. CDs were the first consumer format thatoffered the reproduction quality inherent in a digital audio format. As storageformat, the CD is now recordable (CD-R) as well as repeatedly re-recordable(CD-RW). Depending on the source material, CDs can be used to record andstore music or generic digital data.

The process of getting music on to a CD requires analog to digital (A/D)conversion. The analog audio waveforms produced by music, vocals andother sounds in a space are digitized into analog representations that aregiven specific binary codes of zeros and ones (0’s and 1’s). This coding system is called pulse code modulation (PCM), and it is used in all moderndigital recording and computer audio interfaces. To achieve a faithful repro-duction of audio signals, PCM attempts to make an accurate digital footprintor code of the audio waveform contained in the signal.

The PCM system requires two important elements to function at inaudiblelevels (meaning that the conversion between analog to digital and back toanalog is indistinguishable to the human ear). The first of these elements is sampling frequency, and the second is bit depth.

Sampling frequency describes the number of times that an incoming audiosignal is sampled or measured in a given period of time. CD quality audiouses a sampling frequency of 44.1kHz (44,100Hz). Bit depth describes theaccuracy of the sampling. As analog signals are converted to or from digitalsignals, the measurements are given unique binary codes of zeros and ones(0’s and 1’s). Bit depth corresponds to the length of the binary coded signalsused to describe each sample of the input signal. Longer coded signals allowfor the representation of a wider range of numbers. Smaller coded signalsrepresent fewer numbers and smaller storage requirements. The standardcompact disc system uses a 16-bit system with each sample represented as abinary code 16 digits long. Each of these 16 digits can be either a 0 or a 1; as such there are 65,536 possible combinations (or 216 unique 16 bit codevalues) for each sample.

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The compact disc audio

format is 16 bit and uses pulse

code modulation encoding

sampled at 44.1kHz.

Figure 84. Compact Disc(CD) Logo

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HDCDHigh definition compatible digital format (HDCD) is a technology originallycreated by Pacific Microsonics (a company now owned by Microsoft®). If a CD is encoded with HDCD, the front cover carries the HDCD logo.HDCD-encoded CDs are capable of better sound quality because they areencoded with 20 bits of audio signal data, rather than just 16 bits. HDCDovercomes the limitation of the 16-bit CD format by using a sophisticatedsystem to encode the additional four bits onto the CD while remaining com-pletely compatible with the existing CD format. HDCD provides moredynamic range, a more focused 3-D soundstage, and extremely natural vocaland musical timbre. To listen to the additional four bits of benefit, however,requires a CD player or digital signal processor capable of HDCD decoding.Because of the high resolution digital decoding chips in an HDCD compo-nent, even normal digital recordings (CDs, MDs, DVDs, etc.) can soundcleaner than on normal (non-HDCD decoder) components. Currently, veryfew HDCD audio source or signal processing components are offered inmobile electronics.

DVD-VIDEODVD is an optical storage media format that is primarily used for playbackof movies with high video and sound quality. The acronym DVD stands fordigital versatile disc and encompasses a wide range of applications. A DVD-video disc can contain up to 150 minutes of full motion video in addition toa 2-channel and separate multi-channel audio soundtrack on a single side.This allows continuous playback of most movies on a format just slightlythicker than a standard CD. Depending on the DVD movie title, the multi-channel surround sound audio soundtrack may be a Dolby or DTS-encoded6-channel (5.1) or 7-channel (6.1) soundtrack. Read more on DVD-video in the “Multi-Channel Audio Formats” and “Video Sources” sections of this chapter.

DVD-AUDIO DVD-Audio is not the same as a DVD-Video movie. DVD-Audio (DVD-A) is a DVD format, developed by Panasonic, which holds high quality audiodata. DVD-Audio has been designed to be the next evolution from the 2-channel, 16-bit CD. The DVD-A format is said to provide at least twice thesound quality of an audio CD-on a disc that can contain up to seven timesthe information of a traditional audio CD. DVD-A uses a compression for-mat called Meridian Lossless Packing (MLP) to reproduce its superior audioplayback with a frequency response of 5-50 KHz.

Various types of DVD players that are compatible with DVD-Audio are beingmanufactured for home and professional use. Additionally, many DVD-Aplayers have been specifically developed for the format. Only a few compa-nies have developed a DVD-Audio player specific to the car, but severalmanufacturers have DVD-Audio players in the works. DVD-Audio requires aDVD-A player for true playback of the MLP audio tracks. Some special discsare available that have Dolby Digital or DTS encoded audio material in the

150

Margin Notes


The HDCD 20-bit audio

format requires an HDCD

decoding device; otherwise it

plays as a normal compact

disc.

Figure 85. HDCD Logo

Figure 86. DVD Video Logo

The acronym DVD stands

for digital versatile disc.

Figure 87. DVD Audio Logo

A DVD-Audio disc is not

the same as a DVD-Video disc.

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video zone of the disc. A normal DVD-Video player can access the videozone. Remember that the DVD-A format allows content to be placed in thevideo zone of the disc but does not require it. Many DVD-A discs on themarket today contain only a MLP multi-channel and high resolution 2-chan-nel PCM layer and are thus unplayable on a conventional CD or DVD-Videoplayer.

For the most part, DVD-Audio is limited by the player compatibility issuesand by commercially available titles. Read more information on DVD-Audioin the “Multi-Channel Audio Formats” section of this chapter.

SACD Super audio compact disc (SACD) is a high-resolution audio CD formatdeveloped and supported by Philips and Sony. Like DVD-Audio, SACD offers5.1-channel surround sound in addition to 2-channel stereo mix on a singledisc. SACD uses Direct Stream Digital (DSD) recording, a proprietary Sonytechnology that converts an analog waveform to a Delta-Sigma 1-bit signalfor direct recording, instead of the pulse code modulation (PCM) and filter-ing used by standard CDs. DSD uses lossless compression and a samplingrate of 2.8MHz to improve the complexity and realism of sound.

An interesting aspect of SACD is that it allows dual density, or hybrid discsthat can contain both DSD and CD format (called the red book layer) of thesame music on different disc layers. The top layer holds DSD-format audiodata. This layer is structured so that it can contain both stereo and multi-channel versions of the same music. If the artist, producer or music compa-ny desires, the disc’s bottom layer may contain red book CD-format digitaldata that can be played by any CD player.

When a hybrid disc is placed in an SACD player, the player will automaticallyread to the DSD layer to produce theoretically better sound. A CD player, onthe other hand, would automatically read the bottom red book or CD quality

151

Margin Notes


Am

plit

ud

e (d

B)

Frequency (Hz)

10Hz 100Hz 1K 10K 20K 30K 50K

Frequency Response of DVD-Audio

0DVD-Audio - 5Hz-50KHz

Figure 88. DVD-Audio has a Possible Frequency Response up to 50K

An SACD disc may contain

a CD compatible layer, but the

format does not require it.

Figure 89. SACD Logo

27071_CEA 12/15/05 12:10 PM Page 151

layer. This means that a single disc would provide the best sound quality a particular player was capable of retrieving.

Remember that the SACD format allows a dual density or hybrid disc containing the red book layer but does not require it. Many SACD discs onthe market today contain only a DSD layer and are thus unplayable on aconventional CD player.

Like DVD-Audio, the SACD format can also contain extra information suchas text, graphics and video clips. Also like DVD-Audio, SACD is limited bythe player compatibility issues and by commercially available titles. Readmore information on SACD in the “Multi-Channel Audio Formats” sectionof this chapter.

MINI-DISC (MD)Created by Sony in the early 1990s, the mini-disc is a 16-bit compressed(ATRAC) format. A mini-disc (MD) is a re-writable disc just slightly smallerthan a 1.44Mb computer floppy disc. MD works along similar lines to MP3encoding but takes a different approach in performing the audio compres-sion. It still bases compression on the concept of masking in human hearing,but it only compresses the music to about one fifth of the original size.Current versions can give very high quality playback. Although there are stilla few mobile electronic products that can accept and play MDs, the formathas become integrated into other products along the way such as computersand portable players. Commercially available MDs are difficult to find inmajor music retailers, which contributes to their limited growth market.

COMPRESSED AUDIO FORMATSMany digital audio formats have become popular with music enthusiastswho want their music portable. All of the audio formats in this section areforms of compressing the digital file sizes while trying to remain sonicallyentertaining. MP3 compression is the most popular format, but is by nomeans perfect. MP3 is an abbreviation for MPEG 1, audio layer 3.

Many companies have developed other audio compression formats. Someformats focus on improved audio quality; other formats focus on improvingcompression and shrinking file sizes. Most notably, Microsoft WindowsMedia Audio files (.WMA), Real Audio files (.RM), and Dolby AdvancedAudio Compression (AAC) all use some form of digital compression.

MP3 (as well as WMA, RM and AAC) are lossy compression formats. Duringthe compression process in a lossy format, some of the audio information islost and does not return upon decompression when the music file is playedback. The average listener may never be able to hear the difference betweena high bit rate compressed file and the digital original, but given the choice,many enthusiasts will trade the convenience of digital audio for the purestquality of the compact disc. Until storage sizes increase or other lossless

152

Margin Notes


Figure 90. Mini Disc Logo

Figure 91. Mini Disc

Many compressed digital

audio formats are known as

lossy compression because of

the compromises in signal

fidelity.

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formats (such as DVD-Audio) become more available at competitive prices,lossy compression formats (MP3, WMA and Real Audio) and Dolby AACapplications continue to grow. To read more on the compressed audio techniques and formats, please see the “Compressed Digital Audio” sectionin this chapter.

Mobile Audio Source UnitsHEADUNIT MOUNTING TYPES Whether you are dealing with a cassette player or a CD player, severalaspects of head units are similar. Around the same time compact discs wereintroduced into vehicles in 1984, the industry accepted the DIN-sized head-unit chassis size (7 1/8” x 2 1/8”) as the standard. The adoption of a stan-dard chassis size has allowed the aftermarket industry to develop mountingkits that are easier to work with than in the past, when each manufacturer determined its own sizes. Now the major obstacle in chassis size is the vehicle manufacturer.

A number of other terms relate to headunit dimensions:

DIN - This is the most common aftermarket headunit chassis size. It meas-ures 7 1/8” wide x 2 1/8” high. Many aftermarket radios are actually 7” x 2”and slide into a DIN opening that accepts a 1/8” larger mounting sleeve.There are also many OEM DIN radios including Porsche, Mercedes-Benz,Saab, pre-1996 BMW, most VW and older Jaguar vehicles. Other applicationsinclude some Fords from 1987 and later, most pre-2000 Hondas, and someMazdas. Sadly, DIN openings are disappearing from modern dashboards in favor of unique, more ergonomic shapes.

A DIN opening is 7.125”

wide by 2.125” high.

153

Margin Notes


Figure 92. Front Load DIN Headunit Application

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Oversize GM Chassis - In recent years, GM has put a slightly larger radiochassis into some of the luxury GM cars and trucks. These include someChevrolet, GMC truck, Buick, Oldsmobile and Cadillac models. The openingis nearly double DIN size.

ISO-DIN - The ISO-DIN has a slimmer front panel, sometimes called thenosepiece. This usually mounts into an opening and has a dash trim panelthat fits over the front. An aftermarket radio that can be ISO-mounted needsto have the ability to have the surrounding trim ring removed so only thenosepiece protrudes through the radio opening. Most fixed radios can beISO-mounted. Radios with a detachable faceplate sometimes cannot be ISO-mounted. It depends on the radio trim ring and whether it is fixed orremovable. In a true ISO-DIN installation, the mounting sleeve is not used,but rather the factory bracket assembly is. OEM ISO-DIN cars includeToyota, Mitsubishi, Isuzu, older Nissan and some Mazdas.

Double DIN - Double DIN is the same as two DIN units stacked on top ofeach other. Double DIN could also refer to an opening in a dash, which will allow for two DIN radios to be stacked.

Double ISO-DIN - Much like a double DIN chassis, the double ISO DIN ismeant to accommodate two stacked DIN radio chassis, although it couldalso be a single chassis, double-sized. The key difference between a doubleDIN and a double ISO-DIN is the size of the nosepiece. These openings are found in Toyotas, Mitsubishis and Nissans.

M2000 General Motors Chassis - This is the industry name for the size ofradio found in most General Motors cars. Its front panel measures 8 1/8”wide x 3 5/8” high. The depth of these radios is often very shallow, some-times little more than 5” deep. This can make aftermarket radios difficult toinstall without modifications for limited depth or specialty installation parts.Installation kits for aftermarket radios are widely available to fit nearly every GM-M2000 chassis application.

154

Margin Notes

An ISO-DIN application

does not use the supplied trim

ring, but rather the OEM dash

panel as the trim surrounding

the headunit.


Labeled with "N" and "T"

Figure 93. Factory BracketHoles

Figure 94. Front Load DoubleDIN Headunit ApplicationCommon in Many Ford andMazda vehicles. (Some applications may require dash trim removal)

Figure 96. Standard GM “M2000” Dimension Headunit

Figure 95. Double ISO DINHeadunit Application

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155

Margin Notes


Figure 97. Oversize Dimension GM Headunit

Chrysler Chassis - The Chrysler chassis fits most U.S.-made Chrysler,Plymouth, Jeep and Dodge products. Its front panel measures 7 3/4” wide x 3 1/2” high. It looks about the same as the GM M2000 opening. Chryslervehicles since the late 1990s use the same chassis with rounded corners onthe headunit face. Installation kits for aftermarket radios are available formost Chrysler chassis applications.

Non-DIN Ford Chassis - In recent years, many new Ford and Lincoln-Mercury products also feature a newer and larger chassis size, similar to thedouble DIN size. Since 1998 it is found in nearly all Ford trucks, Lincolnvehicles and many other Ford vehicles.

Figure 98. 1996+ Chrysler Headunits (Identified by Rounded Corners)

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Unique Shapes - An increasing number of vehicles use proprietary integratedcontrol panel (ICP) headunit designs. What used to be limited to a few exoticor luxury vehicles has become more mainstream. Today, manufacturers suchas Ford, Dodge/Chrysler, Honda, Mitsubishi, Toyota, Acura, Audi, Lexus,Volvo, Mercedes Benz, Cadillac, Infiniti, BMW and Nissan all have severalvehicles with unique dashboard shapes and integrated radio/HVAC controlassemblies. In addition, many of these vehicles incorporate an LCD screen to facilitate driver information such as temperature, rear view cameras andOEM navigation systems. With these challenges to consider, some vehiclesare clearly candidates for OEM integration with the factory source unit sothat other functional elements of the dashboard remain intact.

156 THE ADVANCED INSTALLER STUDY GUIDE CHAPTER 3ADVANCED MOBILE AUDIO/VIDEO SYSTEMS

Figure 99. 2000 FordTaurus

Figure 103. 2001 BMW 3Series

Figure 104. 2003 InfinitiG35 Sedan (with OEMNavigation)

Figure 105. 2004 NissanMaxima

Figure 106. 2002 Lexus IS300 Figure 107. 2003 PorscheCayenne

Figure 100. 88-92 GM Trucks3-Piece Source Unit

Figure 101. 2003 HondaAccord (without OEMNavigation)

Figure 102. 2003 HondaAccord (with OEM Navigation)

Source Unit Audio Output Types (Analog and Digital)The vast majority of headunits in mobile audio applications use analog outputs, either powered to directly drive small speakers or pre-amp levelintended to use external amplification. Analog pre-amp level audio outputstypically feature red and white colored RCA connectors. This plug standard isfound on many consumer audio/video products, but in mobile audio these colors represent analog audio inputs and outputs. Nearly all audio

14683_CEA 2/10/04 6:23 PM Page 156

components built for mobile audio applications feature these types of audioconnections. These connections provide the pathway for audio material to getfrom the headunit into other components and, ultimately, to an amplifier.

There are four common types of analog audio outputs: single-ended, bal-anced, floating and differential. This is an important detail with respect tocompatibility of aftermarket and OEM audio components. Often one type of audio output is not compatible with another, even when the componentsplug into each other using RCA audio cables. The majority of aftermarketheadunits with an analog preamp level audio output are simple, single-ended outputs. High-powered headunits that directly power a speaker typically feature a floating ground output. OEM audio systems are often balanced or differential outputs that have other audio grounding conflictsnot directly compatible with single-ended audio inputs and outputs. To readmore about balanced or differential outputs in regard to OEM applications,read more in the OEM integration section of this chapter.

RCA is a plug standard

found on many devices. Red

and white designate preamp

level audio inputs and outputs.

Red is “right”, white is “left.”

157

Margin Notes


Figure 109. SpeakerLevel Outputs

Figure 110. Floating Ground Speaker Output

Some high-end mobile CD players or CD changers feature a digital audiooutput. Perhaps more common is DVD players that feature digital audio outputs. Whenever a source component features a digital output, it must beconnected to an intermediary device called a D/A converter to convert thedigital audio to analog signals that an amplifier can accept. Currently, veryfew mobile audio amplifiers accept digital audio inputs. Furthermore, DVDplayers may need additional decoding of the digital audio signal to unpack

Figure 108. Single EndedPreamp Level Audio Output(Using standardized RCA typeconnectors)

14683_CEA 2/10/04 6:24 PM Page 157

multiple, discrete channels of encoded surround material. For these decodingchores, a digital decoder is required and typically increases the overall costof the audio system.

The vast majority of mobile audio products that contain a digital audio output use an optical connection via plastic optical fiber cable (POF) asopposed to copper wire connections. Optical connections (also called fiber-optic) convert digital signals into light pulses that are virtually immune toelectromagnetic interference (EMI) issues in the vehicle. Optical connectionshave different installation concerns than copper. To maintain signal purity,the optical cable must not be severely bent so that the clarity of the lightpulse is altered in any way. Of course, for any source unit (CD, DVD, etc.) to make use of the optical digital output, it must connect to an intermediaryprocessor that accepts such an input. While this type of input is common onmost home audio components, it is somewhat harder to find in mobile audiocomponents. Optical digital audio connections typically take the form ofTosLink connections between POF cables. The TosLink gets its name fromToshiba, who developed the connector. Most consumer audio products havesince used that type of connector.

When a copper wire is used for digital audio connections, the connector isthe same familiar RCA connector used in analog audio outputs. The onlydifference is that this connection requires a single cable to carry as many as six discrete channels of audio from the source to the D/A converter. Toadequately match one component to another, the copper digital connectionuses coaxial cable between the RCA connectors. This cable typically has a75-ohm impedance at the digital sampling frequencies. Although a digitalaudio cable and an analog audio cable may both share an RCA termination,they are not the same.

158

Margin Notes

The TosLink optical

connector is the most common

in optical outputs in the mobile

environment.


Figure 113. TosLink Optical Connector (Found on plastic optical fiber cables)

Figure 111. Optical DigitalAudio Connection (Use withTOSLink Connector and POF Cable

Top View Front View

Minimum Bend Radius - 1.25"(Approximately 3cm or greater) A digital audio RCA

connector (if present) is not the

same signal as the 2-channel

red and white audio RCA

signals.

Figure 112. Coaxial DigitalAudio Connection Using a SingleOrange RCA Type Connector and75-Ohm Coaxial Cable

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SOURCE UNIT AUDIO OUTPUT CHARACTERISTICSSeveral key points affect the technical performance of any preamp levelsource unit. The individual merit of the source itself (AM/FM tuner,CD/DVD transport and D/A converter, etc.) is important. The preamplifiersection that drives the actual audio output into the next device(s) also matters a great deal. For the most part, these are engineered into the sourceunit and cannot be changed or altered by the installer; however knowledgeof the merits allows the installer to better match system components in theprocess of designing an audio system.

Signal to Noise Ratio (S/N) - This specification describes the differencebetween the audio signal from the source material and any residualnoise generated by the source unit itself. This is measured in decibels(dB) and higher numbers are always better. CD and DVD source unitshave the best signal-to-noise ratios because they have inherently highsignal-to-noise specifications.

Preamp Output Voltage - This specification, measured and listed involts AC, is important for several reasons, the greatest of which involvesthe next component downstream in the signal path. The output voltagefrom the source unit should have enough potential to drive the amplifieror signal processor’s input with the input sensitivity control in the MINposition without overdriving it. This yields the lowest degree of addi-tional system hiss from the amplifier(s). The reference point betweensetting levels using test tones and listening to music generally allows foran easy 2:1 ratio of output voltage to input range. That means if youhave a 4- volt headunit output, it will do just fine when it connects intoan amplifier with a maximum range of two volts. It is always preferableto maximize the signal into the amplifier by matching it with the appro-priate source unit. Although higher voltage is generally better, it musttake into account the next device in the signal path. If the next deviceonly has a maximum range of 2 volts, an 8-volt source unit will almostcertainly overload the input of that next device.

Output Impedance (also called source impedance) - This specification isalso important to consider as you select the components in the signalpath. Output impedance is measured and listed in ohms (Ω). True out-put impedance varies with frequency, so the specification listed with asource unit is typically accompanied by the tested frequency. With out-put impedance at preamp levels, numbers between 50 ohms and 1000ohms or more are found. Although we typically regard lower outputimpedance as better, what is important to remember is that low outputimpedance enables more current. More current is important when driv-ing multiple signal processors and amplifiers in the signal path. If onlyone amplifier is used with a particular source unit, the differencebetween a few hundred ohms compared between two headunits willmake fewer differences than if the system contains multiple amplifiersand preamp level signal processors. Another example of beneficial lowoutput impedance is when Y adapters split the signal from a single output to two or more inputs. This may be common practice in highSPL systems using multiple amplifiers and subwoofers.

159

Margin Notes


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PERIPHERAL SOURCE INPUTSA peripheral source component is considered a source component thatrequires connection to the main headunit in an audio system for commandand control, audio processing or both. The peripheral device(s) can be eitherpermanently installed or portable with the option of easy removal when notused in the vehicle.

AUX InputsMany headunits offer one or more auxiliary or AUX inputs to allow externalsources not contained within the closed loop of the source component audiopath to be added into the mobile audio system. The advantage of a sourceunit featuring one or more AUX inputs is that the external source can have afixed volume and the volume can then be controlled from the front panel ofthe headunit. This is useful for any portable music source, such as an MP3player, or remote mounted source such as a tray load DVD player or videogaming console (X-Box, PS-2, etc.). Headunits that feature the AUX inputalso offer the ability to select the AUX source from the source selection rou-tine in the menu functions or by a dedicated switch on the front panel.

Multiple ZonesMany headunits that feature multiple AUX inputs also allow a dual zonefunction whereby the main audio input selection is routed to the preampoutputs and will be heard on the main speakers. A second zone can be rout-ed to an audio output that feeds signal to a secondary listening device suchas wired or wireless headphones. This feature is especially useful when thevehicle incorporates a rear seat video entertainment system.

Media ChangersThe CD changer has long been a staple in the mobile audio environment.The changer typically connects to a compatible controller headunit or control device via the proprietary bus cable. These bus cables allow thechanger to be controlled and information to be displayed from an alternatelocation, which makes the installation flexibility of the changer virtually limitless with regard to placement. Many changers bundle both audio andcontrol functions into a single cable. Other changers separate the bus (control) cable from the audio by providing a traditional RCA output that must be connected separately.

These days the changers are not limited to only CD playback. Many chang-ers are considered as media changers because they play both CD and DVD-Video discs. Some media changers also offer playback of MP3 files on CD-Ror CD-RW discs. Any changer containing DVD-Video or DVD-Audio play-back capability will feature a composite video output (the yellow RCA plug)in addition to the control and audio cables. DVD-Video playback capabilitymay also indicate the presence of a TosLink optical audio output for usewith a Dolby Digital or DTS decoder. Remember that the optical output

160

Margin Notes

A DVD changer will

typically contain a composite

video output in addition to

control and audio cabling.


14683_CEA 2/10/04 6:25 PM Page 160

must be used if the 5.1 audio playback is going to be enabled and it mustconnect into a decoding device with the capability to decode the appropriate5.1 format.

In addition to disc-based media changers, there have been other changerssuch as cassette tape changers (originally offered by Alpine in the early1990s) and mini-disc changers from several manufacturers.

Hard Drive Storage DevicesA somewhat new alternative for music storage is a hard drive system that canstore many types of media, both compressed and uncompressed. Obviouslythe more compressed the media, the more one can fit on the drive space. Themain benefit is that the configuration of the media as well as the compressionchoices can be managed on a computer, than saved to the hard drive. Thisallows the user to customize his or her selections to suit individual tastes.

Some hard drive systems are contained within the headunit while others areperipheral components that essentially connect as if they were an auxiliarysource, such as a CD changer. Whatever the configuration, the audio outputtypes are no different than most other mobile audio components, so installa-tion of the device does not pose a higher degree of difficulty. If any increasein difficulty exists, it is in the set-up and configuration of the media on thehard drive device.

FM ModulationOne method of getting an external audio source into just about any existingheadunit (either aftermarket or OEM) is the FM modulator. An FM modula-tor takes a traditional audio input (typically in the form of RCA inputs) andbroadcasts that audio signal as an FM broadcast. The FM modulator devicecan be a wired-in version that plugs directly between the vehicle’s AM/FMantenna and the headunit or it may also be wireless.

The FM band(s) that are broadcast via FM modulation are selected to withina bandwidth that has little or no broadcast traffic. Generally the lower rangeof the FM dial is the chosen bandwidth (around 87-89 MHz). Most FMmodulators offer more than one band selection to allow the installer thegreatest flexibility with getting a clean audio signal into the tuner.

If there is one predictable drawback of FM modulation, it is that the audioplayback will only be as good as the frequency response and channel separa-tion of the FM tuner section in the headunit. Even the best mobile tunershave a frequency response that cuts off the extreme low and high frequen-cies of the audible spectrum, so the best source material will still only be asgood as the tuner allows. Some FM modulators compress the incomingaudio signal, which yields better results, but most listeners easily identify thedifference between a direct preamp input versus the same input that hasbeen FM modulated.

Frequency response

and channel separation

are common drawbacks

of FM modulation.

161

Margin Notes


Figure 114. Mobile HardDrive Source Units

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With the FM modulator, only the audio is provided to the headunit, there-fore only volume can be controlled by the headunit. The appropriate stationof FM broadcast must also be selected for the FM modulator to operateproperly. The audio source component still needs its own method of control for functions such as play, pause, track or disc selection, etc.

Headunit Installation ConsiderationsEvery headunit installation has both cosmetic and electronic considerationsthat make or break the installation. With the appropriate installation mount-ing kit (where necessary), wiring harness adapter and antenna adapter(where necessary), installation of a DIN or double DIN headunit is relativelyeasy. Where the difficulty comes is in the following conditions:

The headunit that has been removed has no installation kit availableand the installer must fabricate one.

In this case an installation kit must be fabricated, period. The majority ofinstallation kits are fabricated using ABS or acrylic plastics along with someheating, forming, texturing and/or coloring techniques. Only installers whohave the proper materials and skills should undertake this. The finishedlook must be visually integrated with other dashboard panels.

162

Margin Notes


Figure 115. Typical FM Modulator Configuration

Audio Input(from AUX device)

Audio Output through selected FM Channel

Antenna Input(from vehicle antenna)

Apply +12v and Chassis Groundto activate the

AUX input source

Figure 116. Custom Headunit Insallation from Mild to Wild

Double ISO DIN Installationwith relocated climate controlsand a factory matched texture

ISO DIN Installation in a fullcustom show vehicle installationincorporating dual video screens

14683_CEA 2/10/04 6:25 PM Page 162

The headunit should be ISO-mounted using factory headunit brackets, but no factory headunit is present (either a blank panel ormissing from theft).

Either purchase brackets from the parts department of a car dealer or fabricate them using an appropriate material. Many installers use rear support straps bent to attach to the ISO mount screw locations on theside of the headunit and to the OEM bracket locations in the dash.Angled thin wall steel or aluminum is also an excellent choice. Trial and error will be necessary to ensure a good fit when the panel is completely reassembled.

The factory wiring harness plug has been cut off (either by a previousinstallation or from theft).

This is not really a problem as long as you can function with measurementsmade by your multimeter. If the vehicle had a recent headunit theft, some ofthe power fuses connected to these wires in the fuse panel may have blown,which means they will need replacement before identifying any wires.

1) Begin by setting the meter to DC volts and first identifying a +12vconstant lead, followed by +12v ACC and +12v illumination and/ordimmer wiring.

Note: Use a known good ground point such as the vehicle sheet metal or the negative battery post for a reference ground.

2) After you identify the positive wires, move the meter to the ohmsscale and find pairs of wires showing 2-16 ohms of DC resistancebetween them. These indicate a speaker load is connected to that pair of wires.

3) To find out which speaker in the vehicle it is, use a 1.5v C or D battery to pop the speaker. The speaker moving “up” or “out” corre-sponds to the polarity of the wiring to the battery being correct (the wire on the positive terminal of the 1.5v battery is the positivespeaker wire for that location and the wire on the negative terminal is the negative speaker wire).

Note: In cases where there is no popping and much higher resistancebetween wires (several hundred or thousand ohms), the system is probably amplified and a third party interface device will be necessary.

4) Set the meter back to DC volts and connect the red probe to the wireidentified as +12v constant. Using the meter’s black probe, attempt toidentify a factory ground wire. This is not necessary if you can locate a suitable ground point elsewhere.

Note: If you locate a factory ground, turn on the parking light circuit toensure you have not located a false ground through the dimmer or lightswitch. Many positive lighting circuits appear as ground while theswitch is in the OFF position.

Cut or damaged wiring

harness plugs are one of the

many reasons why test lights

are no longer considered

a safe and reliable tool.

To successfully determine

wire function, use a

multimeter.

163

Margin Notes


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5) Make the appropriate connections to the headunit harness using areliable connection method such as solder and high quality electricaltape or heat shrink tubing.

The factory wiring harness plug is intact but has no wiring harnessadapter available.

This is basically the same procedure as the previous situation, but youshould not cut the plug when interfacing your aftermarket wiring into thisharness. Whenever possible, tap in to the harness a few inches back from the plastic plug so that the original equipment can be reinstalled when necessary. This is especially useful for lease returns or when a customer sells the vehicle and you wish to return it to stock condition.

The headunit contains functions for other parts of the vehicle, such asthe dome light supervision, oil change reset function, door or “lights lefton” chimes, or the OEM security system. Removing the headunit rendersthose function(s) inoperable.

The headunit will either have to remain in the vehicle with an extensionharness to allow it to be placed out of sight or a third-party interface module must be used. Not all lost functions have a third-party solutionavailable, so relocating the OEM headunit may be the only option.

The headunit is part of the on-board telematic system and removalrenders this system inoperable. OEM telematic systems include OnStar,Tele-Aid, Lexus Link, ASSIST and others.

The headunit will either have to remain in the vehicle with an extensionharness to allow it to be placed out of sight or a third party interface modulemust be used. Not all telematic systems have a third party solution avail-able, so relocating the OEM headunit may be the only option. Keep in mindthat the telematic system must still be operational (in the event of an emer-gency) while the vehicle is off and the key is not in the ignition cylinder.

The headunit contains a display that is necessary for other on-boardsystems, such as HVAC control and navigation, to function. Removal ofthe headunit renders these functions inoperable.

Although there may be a custom engineered solution on a case-by-case basis,you should probably consider integration using the OEM headunit.Upgrading the speakers and adding or upgrading amplifiers can make atremendous difference. Perhaps the most important part of this solution willbe the functional integration of the appropriate OEM interface. See the“OEM Integration” section in this chapter for more information.

The headunit is part of an integrated control panel (ICP) that controlsmultiple systems, including HVAC, trip and performance computers,navigation, communications or many other integrated functions.

164

Margin Notes

A telematic unit will need

to remain functional if the OEM

headunit is removed, which

may mean the OEM headunit

must be re-located to another

part of the vehicle. If you are

not certain about an on-board

OEM telematic system, ask

the customer to verify a

subscription service exists

with the capability for roadside

assistance at the press of a

button from within the vehicle.


14683_CEA 2/10/04 6:27 PM Page 164

All but the most advanced installation professionals should definitely consid-er integration using the OEM headunit. Upgrading the speakers and addingor upgrading amplifiers can make a tremendous difference. Perhaps the mostimportant part of this solution will be the functional integration of theappropriate OEM interface. See the “OEM Integration” section in this chap-ter for more information.

Whatever the challenge, headunit installations can range from easy to seem-ingly impossible. The key to a successful installation is having all of the correct installation accessory parts before you begin the installation.

Once a headunit installation has taken place, take the time to check for thecorrect function of balance and, if applicable, fader as well as the clock andpreset memory functions. It is always nice to set the clock and presets forthe customer so the new headunit can get used without delay. Additionally,be sure to wipe down any fingerprints or oily smudges on the dash or thefaceplate of the headunit.

When you deliver the vehicle back to the customer, encourage him or her to read the owner’s manual about the basic operations of the headunit.Although many customers choose the “hunt and peck” method of learningthe button layout of their new component, a quick reference to the owner’smanual will save a lot of unnecessary frustration.

OEM Integration The challenge with connecting an OEM headunit to an aftermarketamplifier- or connecting an aftermarket headunit to an existing OEM audiosystem (whether or not it has amplifiers present)-is that all OEM headunitsand amplifiers do not share a unified audio output style.

Many years ago, mobile audio source units and amplifiers used circuits forinput and outputs, much like home audio systems did. These designs quicklyhad problems, primarily component signal level mismatching and unwantednoise. In addressing these problems, vehicle manufacturers developed theirown ways of doing audio outputs and inputs in a mobile environment. As aresult, not all audio outputs and inputs today can interconnect with one another,and not all aftermarket products will interconnect into OEM audio systems with-out some modifications or application-specific adaptor devices. In the past sever-al years, integrating aftermarket and OEM audio components in harmony hasbeen a growing challenge for all installers, including experienced installers.

Electrically speaking, many styles of audio output are present in OEMsource units and amplifiers. While they all deal with AC audio signals, theactual signal voltage levels and signal reference grounding schemes are dif-ferent across the range of vehicles. Many of these source unit audio outputtypes are dictated by the input style of the factory amplifier(s) when present.In Chapter 2, four OEM audio amplifier input types were characterized.

Always set the clock and

radio station presets when

finishing a headunit installation

so the customer can use the

new headunit right away.

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Low-level, single-ended input - (high impedance typically greaterthan 40 ohms but often in the thousands of ohms).

High-level, single-ended input - (low impedance, typically 2-16 ohmsmeasured between any channel positive and a common negative).

High-level, balanced or “floating” input - (low impedance with highsignal level, typically 2-16 ohms measured between any channel positiveand the corresponding channel negative).

Low-level, differential input - (high impedance with low signal levelcapability and a differential audio input type. Common in Bose systems).

DIFFERENCES BETWEEN SINGLE-ENDED, BALANCED AND DIFFERENTIAL

SINGLE-ENDED SYSTEMSFrom an audio input and output perspective, discrete analog audio signaltransfer between two or more components involves two conductors for eachchannel. The traditional audio output of aftermarket mobile audio equip-ment is to send the audio signal down the inner core of coaxial audio cableand to let it return via the outer braided shield. The majority of mobileaudio equipment using this method also connects the shield to the chassisground of the component. This method of audio output and input is termed“single-ended,” and is regarded as relatively simple.

A simple output stage is needed in the source unit and a simple input stagein the receiving component (such as the signal processor or amplifier). The majority of aftermarket audio components with single-ended outputsand inputs use simple coaxial cables terminated with a two-conductor RCAconnector. On the audio cable, the center conductor that is used to send thesignal can easily pick up interference from external sources, so it is shieldedby the chassis-grounded signal return braid that surrounds it.

Common drawbacks of single-ended outputs and inputs are ground loopsand radiated noises. Regardless of the signal levels (low voltage or high voltage), the inherent problems are still present. As signal levels increase, the ratio of audio signal to unwanted noise improves, which is why many companies offer headunits with preamp level outputs in excess of 3 volts AC.

Expert troubleshooters often can fix ground loops in single-ended systems,yet many installers find ground loops are a frustrating source of noise.Furthermore, radiated noise from high current wiring that is close to single-ended RCA cables is also a constant problem in mobile audio system instal-lations. To best avoid radiated noise, it is essential to avoid running single-ended signal cables near any high current wiring. See the section on“Identifying and Troubleshooting Radiated Noise” in Chapter 2 for moreinformation. Suffice it to say that many vehicle manufacturers easily see thelimitations of single-ended signal transfer in their own OEM systems.

166

Margin Notes


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BALANCED SYSTEMA balanced signal transfer also involves two signal-carrying wires, but neither is chassis-grounded. Instead each carries an audio signal. One conductor carries the same information as the center pin of a single-endedsystem, but the other conductor carries an equal signal that is phase-invert-ed (mirror image) of the audio signal. The wires are typically twisted togeth-er in pairs and the conductor carrying the actual signal is normally called“+”, or non-inverted, and the conductor carrying the phase inverted signal is normally called “-”, or inverted.

In most preamp level balanced systems, there is a third conductor that isintended to connect the chassis grounds of all components together; however, not all OEM mobile audio systems use this three-conductorapproach. The three-conductor approach is highly popular in the profes--sional sound reinforcement industry where audio cables can run hundredsand hundreds of feet; however, the relatively short distances in a vehicle do not necessitate the third chassis-grounded conductor. When only twoconductors are implemented, this is called a floating connection, such ashigh power headunit (speaker level) outputs. In some cases a third conductor may be present but not chassis-grounded, simply functioning as a shield for high frequency noises (such as the switching power supplies of the amplifiers).

In a balanced audio circuit, the audio equipment is more complex. Thesource unit in a balanced system has to generate an inverted copy of theaudio signal and send it along with the usual, non-inverted signal. Thereceiving unit, such as the signal processor or amplifier, has to have an inputstage capable of accepting the inverted and non-inverted signals and recom-bining them back into one discrete signal for each channel.

Many years ago, transformers were used both at the input and output ofmany audio components because it is very easy for a transformer to generateor accept balanced signals. Since transformers are not always cost-effectiveor physically small enough to retain good audio quality, more complicatedschemes are implemented using transistors or integrated circuits (ICs). See “Direct Coupled Differential Systems” for more information.

167

Margin Notes


Figure 117. Single Ended Audio Output

RCA Connector

Shielded Audio Cable

Center Pin(Signal)

Outer Ring(Signal Ground)

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Generating a balanced audio output with high sound quality can be chal-lenging. This explains why many OEM audio systems are not necessarily thesame from vehicle brand to vehicle brand. Many OEM manufacturers simplybolt on a generic phase inverter stage-fed from the main, non-inverted, out-put-to provide the phase-inverted output. This may be cost-effective, but not necessarily high audio quality. The main objective for the OEM supplieris to avoid any major chances for unwanted noises. The balanced systemaccomplishes that aim.

Balanced connections are excellent for noise rejection. When the two audiosignals are recombined in the input stage of the OEM amplifier, they arerecombined by subtraction (the inverted signal is subtracted from the normal signal) using the following mathematical model:

[x - (-x) = 2x]

Where x = the non inverted audio signal

-x = the inverted audio signal

The result is to retrieve the original signal at double strength and to exactlycancel out any radiated noise picked up on the wires.

168

Margin Notes


Figure 118. Balanced Audio Output (Using 2 conductors)

+

-Left ChannelAudio Signal

+

-

Normal Right ChannelAudio Output

Chassis Ground

+

-Right ChannelAudio Signal

+

-

Normal

Inverting

Normal

InvertingInverted

Right ChannelAudio Output

Normal Left ChannelAudio Output

InvertedLeft ChannelAudio Output

Left Channel

Right Channel

(Audio Output Signal Does NOT Reference Chassis Ground)

*Note: At the receiving end of the audio signal (i.e. the next component), a differential operational amplifier must re-configure the NORMAL and INVERTED signals into one single combined signal.

Mobile audio components such as headunits with "high voltage" outputs may already include thedifferential amplifier as part of the output stage to allow function with "unbalanced" audio equipment.

+

-DifferentialAmplifier

+

-DifferentialAmplifier

*See Note

*See Note

14683_CEA 2/10/04 6:28 PM Page 168

DIRECT COUPLED DIFFERENTIAL SYSTEMSMany times, the balanced system (without any transformers) uses a methodcalled direct coupling. Direct coupled balanced inputs are sometimes calleddifferential inputs. One of the shortcomings of differential circuits is thatthey may not always be floating above chassis ground, which means thatauxiliary transformers sometimes must be added to eliminate induced noise(due to ground loops or to very high level noise voltages). The vast majorityof differential systems in OEM mobile audio applications are floating connections, but the relatively low signal levels of some systemsmake successful integration a challenge. In addition to addressing the lowsignal levels, an integration device must also address any differences in the DC offset of the floating audio ground. Many Bose systems in OEMapplications are differential systems.

OEM Interface DevicesLINE OUTPUT CONVERTERSAn important part of integration involves devices specifically engineered tobe middlemen between aftermarket and factory-installed components. Theseinterface devices are line output converters (LOCs). The majority of LOCsused to be engineered and built using basic power resistors (configured as avoltage divider) for the factory headunit output. Potentiometers allowed theoutput signal level to be attenuated enough for an aftermarket amplifier tobe added.

Over the years, as OEM audio systems have changed to include more factoryamplifiers, the complexity of an LOC’s function has also changed. It is not assimple as adding a few large resistors and a potentiometer anymore. Manyheadunit output types will not tolerate the load of a LOC using power resis-tors. The modern LOC also must be able to function as an interface devicethat can adapt aftermarket headunits into OEM amplifiers and speakers.Suffice it to say that all LOCs are not created equal, nor do they all functionin a universal application. Many installation shops will need to have a vari-ety of LOCs on hand to complete installations in different types of vehicles.

Before selecting the appropriate interface device, consider the following fiveparameters:

1. Output and input type

Single-ended

Balanced

Differential

2. DC offset (if any)

3. Grounding

Floating

Common

Reference to chassis

Many Bose systems

use differential outputs and

inputs, which make the

OEM components virtually

impossible to interface to

aftermarket without the

appropriate adapter.

169

Margin Notes


14683_CEA 2/10/04 6:29 PM Page 169

4. Audio signal voltage levels (AC volts)

5. Input and output impedance

To properly match these parameters, use specific interfaces depending on the conditions present at the headunit (or source unit) wiring harness of the vehicle. These interfaces can loosely be divided into two categories:gain/impedance matching interfaces and impedance/grounding schemematching interfaces.

170

Margin Notes

Just about every

installation that retains an

OEM audio component

while having an aftermarket

component installed will

require an LOC of some

sort.


Figure 119. Typical Line Output Converter (LOC) Configuration

* Note - Not all LOC's have active circuitry that require accessory power and chassis ground.

LOCLOCLeft Channel to Amplifier Input

Right Channel to Amplifier Input

Direction of Signal Flow

Left Channel Speaker Level Input

Right Channel Speaker Level Input+

+

-

-

ACC B+*

ChassisGround*

CD/DVD CHANGER ADAPTERSYet another popular upgrade path for an OEM audio system is to add a signal source that is higher quality-and has higher capacity-than what is inthe dash. This is why many customers are interested in adding a CD, MD orDVD changer to their existing factory system. If the customer asks the deal-er, he or she generally will find the cost as much as triple that of a compara-ble aftermarket solution. In most cases, the missing link is simply a protocolconverter or translator that can emulate the correct command from the factory headunit so that the aftermarket changer can be properly controlled.In these cases, the customer’s original unit retains its look and feel and thechanger operates just as the factory option changer would have.

Some CD/DVD changer adapters also offer an additional AUX input for theconnection of a second source on the changer bus line. These devices mayoffer simple RCA inputs that could potentially connect to just about anysource or specifically be configured to connect a second CD changer, satellite radio tuners, etc.

SATELLITE RADIO ADAPTERSIn addition to adding changers, many companies specializing in OEM inter-face products also offer the ability to control a satellite radio tuner directlyfrom the factory unit. The highest level of integration allows the OEM head-unit display to read out the satellite radio stations and informational text.Some adapters are limited to using the audio input of the factory headunit;they rely on an external controller for the selection of stations and text readout. In either case, the specific applications offer the consumer a greaterchoice of entertainment sources than the vehicle’s original equipment does.

14683_CEA 2/10/04 6:29 PM Page 170

TURN-ON LEAD GENERATORSMany OEM audio systems lack a compatible remote turn-on lead for after-market equipment. The remote turn-on circuit from the factory-installedaudio system (if not compatible as a direct +12v turn-on) may fall into one of five categories:

1) The remote turn-on output switches -12v ground rather than +12v positive.

2) The remote turn-on output is positive, but less than +12 volts (like +9, +5, or +3 volts).

3) The remote turn-on output is negative, and less than -12 volts (like -9, -5, or -3 volts).

4) The remote turn-on command is generated by the databus system in the vehicle and cannot be connected to a discrete wire for activatingthe aftermarket equipment.

5) A remote turn-on wire simply does not exist.

Several options are available to remedy these problems, but the easiest solution is the device that senses audio and then generates a suitable remoteturn-on lead. The device is available from many manufacturers and is evenbuilt into several high level input circuits on powered subwoofers. The basicoperation is that the circuit connects to a pair of speaker wires and is able tosense the AC voltage when an audio signal is present. It then generates a+12 volt output that is compatible with aftermarket equipment. The circuitusually will remain on during quiet passages so the amplifiers or signalprocessors do not randomly turn on and off. Some devices offer a fine-tuning adjustment to this time period.

Avoid connecting remote turn-on inputs to the accessory (ACC) circuit. To do so would cause the device to always be on whenever the key is in the accessory position, but to momentarily lose power when the engine iscranking over. This can cause unnecessary pops and thumps in the audiosignal path.

STEERING WHEEL CONTROL ADAPTERSIt is such a shame to lose the function of OEM steering wheel controls whenadding an aftermarket headunit to a vehicle. While most consumers may notconsider the loss of their controls until after the new unit is installed, thereis clearly a compromise for the functionality of the system if the OEM con-trols do not function with the new equipment. In most cases, it is possible to retain the use of the OEM steering wheel controls by adding a third-partyinterface device.

The common connection of the interface device either plugs into a compat-ible wired remote port on the new headunit or, most often, emulates thesame commands that an infrared (IR) remote control does. For this device to function properly, the new headunit must have a wireless IR remote. The steering wheel control adapter essentially is trained to learn the

Turn-on lead generators

are powered devices that

simply take an audio input

and generate a compatible

+12v turn-on lead. Many

powered subwoofers have

this circuit already built

right in.

171

Margin Notes


Avoid connecting the

remote turn-on input for

amplifiers and/or signal

processors to the ACC

circuit of the vehicle.

14683_CEA 2/10/04 6:29 PM Page 171

command from the factory buttons. This connection is hard wired into theappropriate wires at either the back of the radio or near the steering column.Once the factory button initiates the device, the device must learn a commandfrom the remote control. The IR repeater LED must be mounted so that thefront panel of the headunit can receive the transmission from the IR LED.

FM MODULATORSFM modulation, a technique covered earlier in this chapter, is always a lastalternative for getting an auxiliary audio source into the OEM audio system.Remember that there are sonic compromises with FM modulation in theform of both frequency response and channel separation. The FM modulatoris best used for either simple installations, where fidelity is not the primaryconcern, or where there is no other choice.

With the FM modulator, only the audio is provided to the OEM headunit, so only volume can be controlled by the headunit. For the FM modulator to operate properly, the appropriate FM station must also be selected. The audio source component still needs its own method of control for functions such as play, pause, track or disc selection.

OEM Integration Installation ConsiderationsThere are a number of case-by-case installation issues to consider in nearlyall OEM interface installations. As modern vehicles continue to evolve, withmore complex and integrated audio systems, the necessity for strong techni-cal knowledge and good resources only increases. The vast majority of OEMintegration work will require some kind of interface device or maybe more,depending upon the challenges presented by the installation.

Here are the key problems that occur frequently:

Alternator whine noises

EMI related issues

Floor noise / system hiss

Turn-on / Turn-off pops

Turn-on circuit voltage problems

Impedance matching of various inputs and outputs

Signal voltage level matching of various inputs and outputs

Diversity or multi-path AM/FM antennas

Factory-installed telematic system retention

Retaining a portion of the “premium” audio system

The bottom line is that both installers and salespersons need to get into the habit of assuming that whenever a vehicle has some form of OEM integration installation, a portion of the budget should be set aside for theappropriate interface device(s). The biggest challenge with OEM integrationinstallations is that many people assume that if a factory component isretained, the overall cost of installation is less than a complete aftermarket

172

Margin Notes


14683_CEA 2/10/04 6:29 PM Page 172

system. The reality is that approaching OEM integration the right way-usingthe appropriate interface techniques and devices-typically costs more. Thecomplexity of the vehicle and the OEM audio system necessitates an ongo-ing cycle of research and development for interface techniques and devices.No single easy solution applies in all cases. Assuming a heightened level ofcomplexity and cost to perform an OEM integration installation allows boththe installer and customer to be more aware of the task of integration.

Without question, the job of a Professional Mobile Electronics Installer will continue to offer greater challenges in this area and this category willseparate the amateurs from the professionals.

Audio Signal Processing WHAT IS SIGNAL PROCESSING?A signal processor somehow conditions the audio signal when passedthrough it. Signal processors are found in a number of forms, such as:

Equalizers

Active crossovers

Bass enhancement devices

Spatial processors

Digital signal processors (time/phase)

Noise gates

Subsonic filters

Pre-amps

The most common signal processors are crossovers and equalizers. Thecrossover allows signals to be directed at speakers that are meant to handle a particular range of frequencies. It also limits the unwanted or potentiallydamaging frequencies.

The majority of

installations implementing

OEM integration require some

type of interface device to

accomplish the installation

properly.

173

Margin Notes


Figure 120. Signal Flow of Pre-Amp Level Signal Processors

14683_CEA 2/10/04 6:30 PM Page 173

The equalizer (EQ) allows the customer to configure sound to his or hertaste. It also allows for some correction caused by resonance, reflection andsystem shortfalls in the vehicle. The EQ provides a means to accentuate orattenuate a frequency. An equalizer will not fix a poorly designed system orimproperly placed speakers. It is simply meant to flavor the music to soundaccurate and real. Professional equalizers also aim to help achieve a smoothoctave-to-octave balance in frequency response, which further increasestonal accuracy. Signal processors have several important features and functions, depending on the task at hand.

ANALOG VS. DIGITALAnalog EQs use slide bar or rotary potentiometers. This requires a knob orcontrol for each frequency or band. The multi-band versions of these EQsare usually trunk-mounted. Multi-band versions have many bands of adjust-ment, typically about 30 in a mobile audio application. These are known asone-third-octave equalizers. Many professional one-third-octave equalizersare separated into mono configurations, meaning that two are needed, onefor the left channel and another for the right channel. Smaller versions canbe dash-mounted. The smaller versions are usually three to nine bands.

174

Margin Notes

A digital EQ in mobile audio

may have an analog front end

(for the RCA input) and analog

output stage to function with

traditional single-ended RCA

audio inputs and outputs.


EQs are not meant to fix poor

installations, but rather to

enhance an already good

system design.

Figure 121. Graphic vs. Parametric Equalization

Am

plitu

de (d

B)

Frequency (Hz)

Parametric Equalization

0

+6

+12

-6

-12

Q is VARIABLE (Wide to Narrow)

20Hz 100Hz 1K 2K 5K 10K 20K

Band Center is ADJUSTABLE, typically over a range of an octave above or below the center frequency. This reduces the need for a large number of bands.

Boost or Cut

Am

plitu

de (d

B)

Frequency (Hz)

0

+6

+12

-6

-12

Q is FIXED at one value

Graphic Equalization

Band Center is FIXED at one frequencyGreater range of adjustment requires a greater number of bands.

20Hz 100Hz 1K 2K 5K 10K 20K

Boost or Cut

14683_CEA 2/10/04 6:30 PM Page 174

Digital EQs have been introduced to car audio within the past decade. Theadvent of the digital signal processor (DSP) brought forth new possibilitiesfor equalizers. Lower-cost processors now allow for multiple band digitalEQs in the car.

The first benefit to the customer is presets. The customer may have severalEQ curves pre-programmed for sound quality and SPL or for the variety ofmusic they listen to. Displays and controls can be improved aesthetically,because the DSP electronically controls adjustments and needs far fewerknobs. Many DSP devices incorporate other processors besides an EQ. DSPdevices are famous for their ability to delay channels to make listeners feelas though they are sitting toward the middle of the car and in a bigger space.One thing to note: DSPs are not meant to fix poorly placed speakers; theywill just help. It is not uncommon for a digital EQ to feature more than 30 bands. Some advanced mobile audio products have more than 100 bands,which add flexibility as well as complexity to an audio system installation. A digital EQ may have an analog front end and output to allow functionalitywith traditional RCA audio inputs and outputs.

Regardless of analog or digital circuit operation, there are two basic styles ofequalization employed in most mobile audio signal processing components.Graphic equalization features fixed band centers at evenly spaced frequencyintervals; parametric equalization features adjustable band centers and gen-erally adjustable “Q.” Both types of equalization typically offer cut or boostat the desired frequency, although having to do too much cut or boost oftenindicates the acoustic problems in the sound system are better served by fix-ing phase differences, reflections and speaker placement issues. Whetherdigital or analog, graphic or parametric, an equalizer is only able to enhancea well-designed audio system. An equalizer is not meant to fix problemsassociated with poor design, poor speaker placement, phase problems orpoor choices in subwoofer enclosure design. Put an equalizer into place after you have already addressed most of the other system tuning issues.

ACTIVE CROSSOVERSThe crossover, like a glass prism, is intended to separate the different fre-quency bands and redirect them to different components. Without crossovernetworks of some kind, ranges of sound cannot be separated in an audiosystem. As a result, the system will produce nonlinear sonic performanceand intermodulation distortion.

Active crossover networks are designed to be inserted in the signal chainbefore the power amplifier. An active crossover is recognized by its need forexternal DC voltage. It will have external power wires or power terminals.Without power, it will not operate. Many mobile audio amplifiers have built-in active crossover networks to simplify installation and increase flexibility.

Due to bandwidth

limitations, the crossover

is typically the final signal-

processing component

before amplification.

175

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“Q” and SlopesEqualizers are designed to accentuate (boost) or attenuate (cut) at a givenfrequency. Crossovers are designed to attenuate at a given frequency.Adjacent frequencies are also affected to some degree. This is referred to as slope, rate of attenuation, or the “Q” (quality factor). All of these terms describe the same thing: the rate at which neighboring frequencies are affected. Typically, 12dB per octave is used in equalization, sometimes18dB/octave. This means that at 12dB/octave if you were to boost 5kHz by24dB: 10 kHz and 2.5kHz (one octave away in each direction) would be boosted12dB; and 20 kHz and 1.25kHz would not be affected at all. The steeper theslope, the fewer frequencies are affected. The gentler the slope, the more frequencies are affected by either allowing the music signal to pass or block-ing it from passing. Parametric equalization typically offers an adjustmentfor the “Q,” which is why the parametric equalizer is an excellent tool forsystems that simply need a few targeted equalization points not served witha fixed band graphic style equalizer.

Slope is also known as roll-off. The slope of an EQ, crossover or other filter-ing device is measured in decibels per octave (dB/octave) and is indicated asa specific order of response. The following list outlines these orders ofresponse:

Order of Response dB/Octave Roll-Off

1st order 6 dB/octave

2nd order 12 dB/octave

3rd order 18 dB/octave

4th order 24 dB/octave

5th order 30 dB/octave

With active crossovers, higher slopes mean more signal passes (or moreblocked signal) when you measure the next octave away, up or down. Inactive crossovers, 12, 18, and even 24dB/octave are common. In passivecrossovers, simple 6dB to 24dB crossovers are commercially available, many with separate mid/tweeter speakers.

For additional information about slopes of passive crossovers, see the section on “Passive Crossover Networks” in this chapter.

DECODERS FOR MULTI-CHANNEL AUDIO FORMATSWhenever a true encoded multi-channel audio soundtrack is to be repro-duced, the signal must first be decoded. Although this function is typicallybuilt into another signal processing device, it is still necessary to unwrap the multiple discrete channels (or matrix-encoded channels) of audio.Whenever an audio signal is capable of surround sound, for instance, there must be some form of decoding that signal. To read about the differenttypes of surround-encoded material, see the “Multi-Channel Audio Formats”section in this chapter.

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Any type of digitally

encoded audio signal must

have a compatible decoding

scheme as part of the

playback device and

signal path.


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INSTALLATION SPECIFIC SIGNAL PROCESSING CONSIDERATIONSWhen choosing a signal processor for a system, it is not uncommon to haveseveral signal processors or several signal processing functions within onecomponent. Given multiple signal processing paths, be sure to avoid havinga signal over processed.

Whenever a system has a crossover function within one component andanother component is installed (and enabled) with a duplicate crossoverfunction, this is known as cascading. While cascading crossovers can be anappropriate method to increase the roll-off rate of a particular audio signal,the results are less than pleasing if the two crossover points are not symmet-rically aligned. For example, if a headunit has a subwoofer output enabledwhose crossover frequency is 120Hz low pass, connecting into a full rangeamplifier would be absolutely fine because the signal is already filtered. Theproblem arises when that amplifier also has a low pass crossover and it is setto a different frequency. That causes a change in the roll-off that does nothand off the signal with as much accuracy and blend as if there were onlyone crossover point to control. Even if the amplifier’s crossover point is setso that the printed number indicates the same crossover point as the head-unit, there is absolutely no way to know for certain unless the signals ofboth components are measured and calibrated individually before cascadingthe crossover points on top of one another.

Another concern is overlooking a subsonic (or infrasonic) filter for certainsubwoofer enclosure types. In any vented enclosure, the woofer literallybecomes uncontrolled below the frequency at which the vent, or port, istuned. At that point, it is as if the subwoofer is not even in an enclosure. Toprevent any unnecessary speaker failures and to increase power handlingabove the tuned frequency, use a subsonic filter. This provides a high passfunction at a very low frequency, so that the very lowest frequencies (25Hzand lower) are simply cut off from the bandwidth reproduced by the sub-woofer amplifier. By cutting the damaging low bass away from the ventedenclosure, the speaker avoids damage from over excursion and excessiveamounts of heat in the voice coil. A subsonic filter can save a subwooferwhen implemented correctly. Many subwoofer amplifiers and activecrossovers feature subsonic filtering capabilities.

Mobile Audio Amplifiers In a mobile audio environment, an amplifier has two distinct sections, thepower supply section and the audio section. The power supply section con-tains components for filtering the vehicle battery voltage before it moves onto step-up transformers that increase the voltage for amplification. Step-uptransformers trade an increased output voltage for an increase of input cur-rent. Larger output power requires more input current.

In the power supply section, capacitors help to stabilize the supply voltagelevels. The addition of externally mounted power supply capacitor(s) canoften help the stability of the power supply. Of course the vehicle must beable to support the power supply requirements in the first place.

Use a subsonic (infrasonic)

active filter when installing

vented enclosure designs. The

filter may protect the speaker

from unnecessary damage at

points where power handling

is at minimum.

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Avoid cascading multiple

redundant active crossovers

where different crossover

points exist. It is virtually

impossible to align multiple

active crossovers by ear

without the assistance of an

RTA or oscilloscope with a

signal generator.

Mobile audio amplifiers

have two distinct sections,

power supply and audio

input/output.

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Regardless of amplifier topology, the power supply section in any 12-voltamplifier affects overall efficiency. Since vehicle electrical system voltage mustbe stepped up into larger voltages before it can be useful for audio amplifica-tion, it creates an intermediate step that wastes power and reduces overallefficiency. The drawback of inefficiency is, of course, heat. An amplifier thathas a more efficient operation will produce less heat for a given level of out-put power. As amplifiers are asked to drive lower impedance loads (say goingfrom 8 ohms to 4 ohms - then 4 ohms to 2 ohms - then 2 ohms to 1 ohm),power supply efficiency typically suffers because of the increased amounts of current draw in the power supply section.

The audio section of a mobile audio amplifier processes the audio signalinput-typically fed by a low level RCA jack or by high level speaker inputs-to the audio output stages. Eventually, speakers are connected to a highervoltage version of the audio signal that was input into the amplifier. Highervoltages are available from the power supply but need to be switched intothe speakers in a way that represents audio that will move a speaker in andout. This is why audio inputs and outputs are classified as AC. There is analternating motion of both the signal and the speaker to which the signal isultimately connected. It would be impossible to reproduce music throughspeakers by simply connecting a speaker to high voltage DC. Depending onpolarity, the speaker would simply move all the way out-or in-and stay thereuntil DC is removed. The amplifier alternates the polarity so the speakermoves both in and out. It must do this rapidly enough to keep time with the audio signals at the input.

In an output stage of an amplifier, the job of driving the speaker is splitbetween two sections, or rails. Think of each rail as a garden hose faucetthat can be turned all the way off, full blast or anywhere in between. Onesection, or rail, provides the positive part of the signal when the speaker ispushed out. The other rail provides the negative part of the signal when thespeaker is pulled in. These two rails are composed of power transistors.Each rail can deliver a variable fraction of the available supply voltage.

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Margin Notes


Figure 122. Inside a Mobile Audio Amplifier

14683_CEA 2/10/04 6:31 PM Page 178

The amount of voltage available to the rail is the rail voltage. The differencebetween amplifier classes has to do with the way the design changesbetween the positive rail and the negative rail and vice versa.

Channel ConfigurationsThroughout the mobile electronics industry, amplifiers from one to eightchannels of output are available. In determining a consumer’s needs, thenumber of amplifier channels is just as important as the output power. Youcan configure channels in different ways for different applications. Forexample, a four-channel amplifier can have two channels bridged while theremaining two channels operate in stereo. This creates a three-channel sys-tem. A six-channel amplifier can have two channels bridged while theremaining four operate in stereo. You can accomplish any number of combi-nations with multi-channel amps. For example, you can use a four-channelamp in three-channel mode, where the low pass crossover sends bass to themono channel for subwoofer input, while the remaining stereo signal drivesa pair of components in the doors in a high pass mode.

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Margin Notes


Figure 123. 2, 4, and 6 Channel Amplifier Default Configurations

4 Channel Amplifier

6 Channel Amplifier

2 Channel Amplifier Front OR Rear Speakers

Front Speakers

AdditionalSpeaker Locations

Rear Speakers

Front Speakers

Rear Speakers

Bridging ChannelsTwo main factors limit the output power in a common two-channel mobileaudio power amplifier:

The impedance of the speaker(s) connected to the amplifier

The internal power supply voltage

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Assuming the best variables in the vehicle electrical system, these two factorsstill determine the safe and reliable power output of the amplifier. Other thanbuying a more powerful amp, one has limited choices to obtain more power.

You can reduce the load impedance, but if the load happens to be a pair ofstandard loudspeakers, this is not always viable. Since the impedance of eachspeaker is already a fixed value, adding speakers in a parallel connection willeffectively reduce the impedance loaded on each amplifier channel.Depending on the design, some amplifiers may not have enough outputdevices to effectively dissipate the added workload (i.e., heat).

Increasing the power supply voltage by exchanging power supply compo-nents is generally a bad idea, since most commercially available power amps do not have a wide safety margin with component ratings. Amplifiersare engineered with specific parts in mind for the intended application.Modifying the power supply of an amplifier may cause destruction if thepower supply voltage is raised to obtain even 50 percent more power at the given load impedance.

Bridging an amplifier can cause it to produce almost four times the power ofa single channel for the same impedance, however there are electrical andthermal costs for doing so. Bridging combines two channels into a single,more powerful channel. Bridging is often a more reliable way to achieveincreased power levels without sacrificing impedance stability.

Normally, a speaker is driven from the positive amplifier output to signalground and the AC voltage swing is limited by the maximum rail supplyvoltage in the amp. Consider a 100-watt (RMS) per channel power amp:100w into 4 ohms requires a signal voltage of 20 volts RMS.

P=V2 / R or 20 volts2 = 400 / 4 ohms = 100 watts

To achieve this, the peak rail voltage is just over +/-28V (20*1.414), and a power supply voltage of about +/-35V will generally be used to allow forlosses due to heat and switching as well as supply voltage variations. For this 100-watt example, the voltage measured across the speaker voice coil terminals is about 20 volts RMS.

The same amplifier into 2 ohms will deliver close to 200 watts per channel,provided the power supply does not collapse under the extra workload. For both of these examples, in each channel only one side of the loudspeak-er is driven, and the other is connected to the signal ground of the amplifier.In a high-powered amplifier, the audio signal ground is not common withchassis ground, but instead floated above the chassis ground potential. This is where the term “floating ground” comes from. Nearly all aftermarketamplifiers use this design.

Bridging channels means the second amplifier channel is configured so thatthe output is exactly 180° out of phase (inverted), with the first channel

180

Margin Notes

Bridging an amplifier

allows it to produce almost

four times the single channel

4-ohm power, but doubles

current draw and significantly

increases heat generated on

the heatsink.


An amplifier’s bridging

capabilities depend upon the

load impedance connected to

the output terminals and

internal power supply voltage.

14683_CEA 2/10/04 6:32 PM Page 180

then connected to the signal-grounded (negative) side of the speaker. As onespeaker terminal is driven positive, the other is driven negative by the samesignal level, only the signal level is 180° inverted. This creates an overalllarger voltage range across the speaker coil, essentially double the initial rail voltage.

At maximum power, the 4-ohm loudspeaker now sees double the voltagethat it would receive from one amplifier channel alone. Using the same for-mula, observe the effective increase in power by simply doubling the voltageacross the speaker coil.

P=V2 / R or 402 = 1600 / 4 = 400 watts

As the voltage across the speaker coil doubles, the current through the voicecoil (and amplifier rail output devices) also doubles. This is the reason thateach amplifier channel must be capable of driving half of the normal speakerimpedance. For example, if an amplifier is capable of running in 4 ohmsbridged mode, it must also be able to run 2 ohms stereo. Although it is notthe same load, it produces the same heat and current on the output voltagerail. The main difference is that when bridging, one channel is a mirrorimage inverted version of the other channel.

181

Margin Notes


Figure 124. How an Amplifier Works in Bridged Mode

Amplifier

Sample Specifications100 Watt x 2 @ 4 Ohms 400 Watt x 1 @ 4 Ohms

Subwoofer

*Bridging Combines +/- Rail Voltage to provide all of onechannel as (+) Voltage and all the other channel as (-) Voltage

Left Channel@ 4-Ohms

+ 20v

- 20v20 Volt Rail

(Swings +20v and -20v)

Right Channel@ 4-Ohms

+ 20v

- 20v20 Volt Rail

(Swings +20v and -20v)

Bridged Channel@ 4-Ohms

40 Volt Rail(*Swings +40v and -40v)

+ 40v

- 40v

Bridged Mode

2 Channel Mode

P = E2 / R

2 Channel Mode E = 20v total per channelR = 4 Ohms202 = (20 x 20) = 400400 / 4 = 100 Watts/Ch.100 Watts x 2 Channels

Total Output = 200 Watts

Bridged Mode E = 40v across one channelR = 4 Ohms402 = (40 x 40) = 16001600 / 4 = 400 Watts400 Watts x 1 Channel

Total Output = 400 Watts

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Bridging amplifier channels is very common in mobile audio systemsbecause the nominal 12-14v of a vehicle electrical system is too low toobtain large amounts of amplifier power without using ridiculously lowimpedances. Whether running stereo or bridged mode, an amplifier thatdelivers several hundred watts must still have stable input voltage andcurrent to deliver that power level reliably. In addition, be cautious in bridg-ing amplifiers where heat dissipation is a concern. If an amplifier runs hot ina 4-ohm stereo application, it will run four times hotter (or reach thermalshut down four times faster) when it is running bridged without additionalthermal management, such as fan cooling.

Mobile Audio Amplifier Circuit Topologies CLASS A AMPLIFIERSClass A amplification is also known as linear amplification. In a true Class Aamplifier, the transistors of the positive and negative rails are always on atthe same time, regardless of whether the output is positive, negative or zero.This means that a lot of power gets wasted as heat. True Class A amplifiersare rare in mobile audio because they consume so much energy for such lowoutput. Some respected audiophiles praise the sound quality of a Class Aamplifier as clearly distinguishable over other designs, although in truth it is very difficult to hear subtle sound quality differences of amplifiersin a vehicle with road and wind noises.

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Margin Notes


Figure 125. Class A and Class B Amplifier Operation

Positive Rail

Negative Rail

Rail is ONLY "ON" with Signal

Audio SignalON

OFF

OFF

ON

ON

OFF

OFF

ON

Rail is always "ON"

Positive Rail

Negative Rail

Audio SignalON

ON

ON

ON

ON

ON

ON

ON

Class A

Class B

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CLASS B AMPLIFIERSClass B amplification is also known as linear amplification, but the Class Bamplifier approaches audio output in a different manner than the Class Adoes. In a true class B design, the positive and negative rails are completelyoff until a signal comes through. If the signal is positive the positive block railis powered on. Conversely, when the signal changes to negative, the positiverail turns off and the negative rail turns on. The two rails are never on at thesame time. There is no power loss when there is no signal, but the handoffbetween the positive side and the negative side is a bit rough. The transitionfrom one to the other causes crossover distortion that is obvious at low lev-els. Though Class B has inherent high fidelity limitations, many brands ofmobile amplifiers are true Class B designs. Class A provides more outputpower for a given amount of electrical consumption, while Class B has limited fidelity compared to Class A.

THE CLASS AB HYBRID AMPLIFIERClass AB hybrids combine the good from both Class A and Class B designswhile seeking to eliminate the drawbacks from each. When there is no signal,the positive and negative rails are both “on” a little bit and both faucets are“on” a little. Some power is wasted, but not nearly as much as in a straightClass A. When the signal goes positive, the negative rail stays on for a brieftime while the signal gets bigger. Once the signal is strong, the negative railshuts off, as in Class B. In a similar way, when the signal goes negative, thepositive rail stays on until the negative signal is sufficiently strong. This over-lap prevents the crossover distortion present in a straight Class B design.

The drawback to Class AB is that the overlap, known as bias, has to beadjusted for every channel on the amp. The bias adjustment needs to be seton each amplifier that is manufactured and the work is more labor intensivesince it is done by hand. There are many examples of Class AB hybrid amplifier designs throughout mobile audio.

The majority of full range

amplifiers in mobile audio are

Class AB hybrid designs.

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Margin Notes


Figure 126. Class AB Hybrid Amplifier Operation

Positive Rail

Negative Rail

Rail stays "ON" just after Signal

Audio Signal

Class AB

ONOFF

OFF

ON

ON

ON

ONOFFOFF

ON

ON

ONON

ON

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CLASS D AMPLIFIERS (SWITCHING AMPLIFIERS)Although switching amplifiers are offered under many names, Class D is themost common. Marketing departments have invented several new classeswith new alphabet letters attached. In spite of the hype, these have all beenvariations on the same basic theme. The term “switching amplifier” will beused here to refer to all of these.

While traditional linear-operation amplifiers work by supplying a variablefraction of the power supply voltage to the output, a switching amplifier, asthe name implies, uses switches to deliver output power. A switch is eithercompletely open or completely closed. To use the water faucet analogy, thefaucet is either off or opens full blast.

A switch essentially wastes no power. A light switch in a home can controlhundreds of watts of electrical power and not even get warm. The same positive and negative power supply voltages that are present in conventionalamplifiers are also present in switching amplifiers. The middle pointbetween these plus and minus supplies is called the signal ground and isused as a reference point. A switch connects between each of these suppliesand the power output. Basically they connect in series across the positiveand negative supplies.

If both switches are closed circuit at the same time, a short circuit across the power supplies would result. As installers know, a short circuit causesinfinite currents to flow, damages components and blows fuses. When thepositive switch is closed, the negative switch is open, and vice versa. A closed switch delivers nearly 100 percent of the supply voltage to the output. The switch can deliver either full positive supply or full negativesupply, depending on the voltage rail to which it is connected.

184

Margin Notes


Figure 127. Class D Amplifier Operation (*Each Duty Cycle Equals a Value thatTranslates into a Signal Voltage)

Positive RailModulation

Negative RailModulation

Signal is Modulated in ON-OFF Duty Cycles*

Audio Signal

Class D

ON

ON

14683_CEA 2/10/04 6:33 PM Page 184

At this point, the rail voltage switching is relatively efficient, but the outputdoes not look much like audio on an oscilloscope, nor would it sound likeanything. You can get audio output from a switching amplifier by varyingthe amount of time that the positive switch is closed compared to the timethe negative switch is closed, and then using the average value of theswitched output. The averaging process is done by looking at the positiveand negative output times.

The polarity of the output is determined by which value is bigger. If the positive switch is closed for a longer time than the negative switch, the average value of the output is positive. If the negative switch is closed for a longer time than the positive switch, the average value of the output isnegative. Finally, if the switches are closed for an equal amount of time, theaverage value is zero. When the positive and negative areas are equal, theycancel each other out.

Here is an averaging example:

Suppose the positive and negative outputs each have a height of one and theoutput is positive for 7 1/2 seconds and negative for 2 1/2 seconds. The areaof the positive side is 7 1/2 and the area of the negative side is 2 1/2.Subtract 2 1/2 from 7 1/2 to get 5. So the net output is +1 for 5 seconds andzero for 5 seconds - in this 10-second period, the average value is + 1/2.

How does the amplifier get an electrical average? Use a low pass filter, whichgoes between the switched output and the amplifier output. This filter usesinductors and capacitors. It removes the rapid changes from positive to neg-ative and back, giving us the average as output.

Now the amplifier has a way to get any value of output. But how does thatbecome audio? A circuit called a pulse-width modulator takes audio signalinput and creates signals that control the positive and negative switches. The switches do their thing, creating positive and negative outputs, and then the low pass filter gives back the original audio signal.

The power switches have to operate at a frequency that is higher than thehighest audio frequency to be reproduced. This is due to the averaging ofthe low pass filter. It takes several cycles of switched signal to get an averagethat accurately represents the audio signal at a given time. In a typicalswitching amplifier, the switching frequency must be at least 10 times abovethe highest audio frequency. So, during one complete cycle of audio signal,the amplifier will have at least 10 cycles of switching.

How does the efficiency of a switching amp compare to a conventional linearamp? At full rated power, the difference is not that incredible. Where switch-ing amps really produce greater efficiency is at medium power. For example,looking at just the output stages, at 1/4 of rated power, the linear amp hasjust over 40 percent efficiency, where the switching amp has about 70 percent efficiency. This matters because music spends most of the time in between minimum and full power.

185

Margin Notes


Figure 128. CEA PublishedStandard for Mobile AmplifierPower Output. The PrimaryMeasurement Criteria Outlinedin CEA-2006 are Power Output,the Signal-to-Noise Ratio andTotal Harmonic Distortion PlusNoise (THD+N),

14683_CEA 2/10/04 6:33 PM Page 185

The efficiency picture in a car is more complex because you must have apower supply as well as an amplifier. The battery voltage must be convertedto a higher voltage before it can be used it to make audio. This intermediatestep wastes power and reduces efficiency in both linear and switching ampli-fiers. While you may hear claims of 80 to 90 percent efficiency in switchingamps, this is for the audio output only. By the time the power supply ineffi-ciencies are added in, a car-switching amp really demonstrates about 65 to75 percent efficiency. This compares to between 45 and 55 percent for a linear amp. Remember that these numbers are at full power and the difference is even greater at medium power.

Some marketing people have observed that the rectangular signals that comeout of the power switches look like the string of “1’s” and “0’s” of a binarydigital signal and have proclaimed that switching amplifiers are “digital.”The confusion is understandable, but this is wrong. Digital audio uses astring of numbers in which each number represents the approximate size ofthe audio signal at a given time. When you convert the string of numbersback to audio, you get a signal with stair steps. You cannot have a digitalvalue between two whole numbers. There is no digital “1 1/2”, only “1” and “2.” That is where the “approximate” part comes in. The technical term is “quantization.”

In a switching amp, the modulator can make infinitesimally small changes to exactly represent the audio signal in pulse form-no stair steps, no quanti-zation-and no string of binary code as in 16-bit PCM audio. The next timesomeone calls a switching amp “digital”, just smile and explain this.

If switching amps are so cool, why are not all amps made this way?Switching amps require high-speed switching devices that are rugged andeasy to use. They did not exist until the early 1980s when power MOSFETsappeared. Then, too, the design problems in a switching amp are completelydifferent from those in a linear amp, so there is a big learning curve. And aswitching amp has performance tradeoffs. It is easy to get good efficiency,but hard to get low distortion, low noise and good damping factor. Newresearch is going on today to eliminate these tradeoffs, so you can expect tosee switching amps become more common in the future.

The following terms apply to amplifier power (AC voltage) measurements:

RMS - root-mean-square. Compute the RMS voltage of a signal bysquaring the instantaneous voltage, integrating over the desired time,and taking the square root. If the signal is only AC, then the single peakvalue multiplied by 0.707 will work. As an example, if the voltage on anoscilloscope is 10V peak, then the RMS value is 7.07 volts RMS. Thevalue of an RMS measurement is that it represents something likely tobe measured at any given time, rather than just one reading over theentire measurement such as the peak measurement.

186

Margin Notes


Class D amplifiers (by

switching design) are not “

digital” as some literature

mistakenly says.

14683_CEA 2/10/04 6:34 PM Page 186

Average - The average voltage of a signal is the mathematical averageof the absolute numeric value of all points. Averaging improves theaccuracy of measurements. In RMS measurements, averaging is inherentin the measurement; however true averaging takes into account theamount of time over which the measurement is made.

Peak - Peak is the maximum instantaneous voltage of a waveformover a given observation period. Peak is often the most “complimenta-ry” measurement and a manufacturer lists it on the chassis of a compo-nent, in advertising materials or on product packaging. Peak can becomputed from an RMS value by multiplying RMS x 1.414. For exam-ple, if the voltage on a true RMS oscilloscope is 10V RMS, then the peakvalue is 14.1 volts peak.

Peak-to-Peak - The voltage from negative peak to positive peak of awaveform.

Continuous - The sustainable voltage or signal level over a long periodof time. Typically, the continuous rating considers the normal amount oftime in which the rated device(s) are used.

Passive Crossover NetworksWhen a filter network is placed after the amplifier, it needs no electricalpower for any of the components to operate. Only an audio signal is needed.These filters are known as passive filters.

Passive crossovers are simple networks that are designed to pass high signallevels. They are inserted between the power amplifier output and the driv-ers. Passive crossovers require no hook-up to the vehicle’s electrical systemand divide the sound ranges after they exit the amplifier. Two and three-waycar audio speakers typically include a simple form of passive crossover in theform of a single capacitor to “block the bass” to the high frequency part ofthe speaker. The installer can design and assemble passive crossovers to pro-vide specific characteristics needed. Four main crossover functions are inuse for mobile audio system installations:

Low pass crossovers let low frequencies pass through and primarilydirect bass ranges to the components operating the subwoofers.

High pass crossovers only allow higher frequencies to pass for routingto high frequency drivers.

Bandpass crossovers allow a middle-range bandwidth, the “passband,” to pass through. Such applications typically apply to mid-rangespeakers covering many octaves. In some cases, a bandpass crossover(or filter) will be used to let the entire musical band pass, but not sub-sonic and ultrasonic frequencies. Narrow bandwidth bandpass applica-tions apply to dedicated midbass speakers and subwoofers with bothlow pass and subsonic (high pass) filters.

A notch filter performs the opposite function of a bandpass filter. It cuts out or notches a particular band and compensates for acousticpeaks.

Passive crossovers go

after the amplifier but before

the speaker in the audio signal

path.

187

Margin Notes


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Although any of these crossover types can be active or passive, many com-ponents in car audio use passive crossovers for the cost savings of additionalamplifier channels without much sacrifice to the quality of the sound. Ingeneral, passive crossovers are much more common for mid-range andtweeter speakers than for subwoofers.

188

Margin Notes


Figure 129. Typical Crossover Frequency Response

Am

plit

ud

e (d

B)

Frequency (Hz)

0

-6

-12

High Pass

20Hz 100Hz 500Hz 1K 2K 5K 10K 20K

-18

Am

plit

ud

e (d

B)

Frequency (Hz)

0

-6

-12

Low Pass

20Hz 100Hz 500Hz 1K 2K 5K 10K 20K

-18

Am

plit

ud

e (d

B)

Frequency (Hz)

0

-6

-12

Band Pass

20Hz 100Hz 500Hz 1K 2K 5K 10K 20K

-18

Am

plit

ud

e (d

B)

Frequency (Hz)

0

-6

-12

Notch Filter

20Hz 100Hz 500Hz 1K 2K 5K 10K 20K

-18

Figure 130. Zobel Network

Resistor

Non-PolarCapacitor

-

++

-

AmplifierOutput

Note - If using a passive crossover network, place BEFORE the Zobel Network

OTHER PASSIVE NETWORKSIn mobile audio installations, other crossover types can be useful as a correction circuit to compensate for certain interactions between the speak-er, crossover and vehicle. Since a passive crossover is highly phase-sensitiveand the vehicle can cause phase problems, the phase correction circuit canreturn the front wave to a uniform output.

Response-shaping filters, similar to notch filters, allow for correction inacoustically or electrically generated peaks. The common Zobel network isintended to remove the resonant impedance peak that is inherent in allwoofers, mid-ranges and tweeters.

14683_CEA 2/10/04 6:34 PM Page 188

Driver attenuation circuits will balance the output from two or more driversfor optimum linearity in output. They reduce the output of a driver to matchthe overall volume.

Each system can have custom-tailored crossovers. Since they are connectedjust before the speakers, one amplifier can drive a number of speakers cor-rectly. This allows for the design of systems that are simple, yet provides foreasy and effective upgrades just by adding amplifiers.

CONSTRUCTION OF A CROSSOVERCrossovers are built according to mathematical models that represent certaintypes of sonic behavior.

Active crossovers are the most efficient, but require more than one amplifierto reproduce the various ranges. Since crossovers operate in the preamplevel area of the signal, efficiency is high, and most active crossovers arevariable for instant adjustment of sound parameters. Despite the higher costsinvolved in a multi-amp system, when coupled with active crossovers, thesound is optimized. Many amplifiers feature both active crossovers (built in)and multiple channels, making it cost less overall to implement an activecrossover than to use separate outboard components.

Fundamental electronic components known as capacitors and inductors areused for passive crossover networks due to the way they control frequencies.Resistors are used in some of the more exotic crossover networks and arealso used in notch filters, Zobel networks and driver attenuation circuits.

Capacitors have unique properties that make them extremely valuable tomobile electronics and audio equipment in general. A capacitor can store acharge for a short period of time and, therefore, will take in noise and ripplein a voltage and release it later as smooth, steady voltage. In series with adevice, a capacitor will pass AC but will not pass DC. A capacitor willalways try to charge up to its working voltage. If you exceed the workingvoltage, the capacitor may possibly explode. When presented with an audiosignal, a capacitor will pass only the frequencies that its value will allow. Aslower values of capacitors are used, higher frequencies are allowed to passthrough the capacitor. This is called capacitive reactance, which causes high-er resistance at lower frequencies.

Coils (inductors) exhibit nearly the opposite effects of capacitors, but alsohave some of their own unique properties. Inductors pass steady DC but willnot pass AC. Rapidly pulsating DC will be amplified to a high voltage for a brief period until the pulsations begin to saturate the inductor. At thatpoint, the inductor will block the voltage. When voltage is first delivered to or interrupted from an inductor, it will increase the voltage for a briefinstant (like an ignition coil on a car). When voltage is first delivered to an inductor, it will produce a magnetic pulse around itself. Two or moreinductors wrapped around the same core will alter AC voltage from one coil

Passive crossovers

are made up of non-polar

capacitors and/or inductors.

Other passive filter networks

may use power resistors

as well.

189

Margin Notes


Figure 131. Axial and RadialElectrode Capacitors

Radial Electrodes

Axial Electrodes

14683_CEA 2/10/04 6:35 PM Page 189

to another. This is the basis of a transformer. Transformers will also convertimpedance between two mismatched components.

When presented with an audio signal, an inductor will pass only the fre-quencies that its value will allow. This is opposite to how a capacitor func-tions. As higher values of inductors are used, lower frequencies are allowedto pass through the inductor. This is known as inductive reactance, whichcauses higher resistance with higher frequency.

These passive components are highly inefficient at lower frequencies due toinsertion loss. They also can create phase distortions that can have a dramat-ic effect on the quality of sound as volume increases. Passive crossover com-ponents can vary in tolerance and quality, which can change the frequencyof the crossover points of your drivers and can affect the amplitude of eachof these frequencies as they interact in the crossover region.

This can cause some frequencies to be delayed with respect to other frequen-cies. This delay is called phase-shift. This is particularly important with thetweeter crossover, where only high quality capacitors should be used. A tol-erance of +/- 10 percent could change the crossover point by 500 Hz ormore, causing either major frequency interaction between the tweeter andmid-range, or a 2 dB to 3 dB acoustic “hole” to occur at the crossover point.

Phase-shift is inherent in most passive crossovers, and some designs (such asthe third-order Butterworth) can change the radiation angle of the loud-speakers to be off-axis.

Crossovers are usually referred to by the name of the inventor or by themathematical model that the crossover represents. The most common typesare the Butterworth, Chebychev, Bessel, Bullock Equal Compromise (BEC)and Linkwitz-Riley

Butterworth filters are known for their flat frequency response and limitedtendency to create peaks. A second-order (12 dB per octave slope)Butterworth reduces the demand on the loudspeakers but operates 180° outof phase. Reversing the tweeter polarity in a two-way system and the mid-range polarity in a three-way system overcomes this problem. A third-order(18 dB per octave slope) Butterworth filter results in fast roll-off and correctphase in either polarity but does not accept the use of time delays for cor-recting problems caused by speakers not radiating on the same verticalplane. A fourth-order (24 dB per octave slope) Butterworth returns the samephase problem as second order and is quite inefficient at lower frequencies.You can find Butterworth filters in many crossover component charts frommanufacturers as well as on various websites.

The Linkwitz-Riley filter in fourth-order configuration minimizes interactionbetween drivers due to its steep slope, while maintaining correct phase andallowing time correction for drivers that are not on the same physical plane(time aligned). This crossover yields the best sonic performance above 3kHz over other configurations.

190

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ORDERS OF RESPONSEThe order of response for a crossover is its degree of effect on the signal. Ahigh ordered filter does its job within a narrow segment of the musical band.A low ordered filter reacts much more smoothly but does not attenuatequickly enough for some applications.

The “order” is a measure of attenuation measured in dB. A 6 dB filter willreduce the output of the signal by 6 dB every time the octave doubles orhalves. For example: a signal at 100 Hz will be reduced in volume 6 dB at200 Hz and 12 dB at 400 Hz, etc.

The number of orders is the quantity of equal 6 dB attenuation effects on theaudio signal passing through the filter network. A second order crossoverattenuates at 12 dB per octave. For example: a signal at 100 Hz will bereduced in volume 12 dB at 200 Hz and 24 dB at 400 Hz.

Different orders of filter are created by simply cascading basic filters. A firstorder filter has either a single inductor on the woofer (for low pass applica-tions) or a capacitor on the tweeter (for high pass applications). Secondorder filters have one of each component on the woofer and tweeter. Thirdorder filters have two capacitors and a single coil on the tweeter (for highpass applications), while the woofer has the opposite (for low pass applica-tions). Fourth order filters have two of each component.

Note: With passive components it is easy to cascade components becausethe component values are decided before the passive filter is constructed.Active crossovers, on the other hand, are difficult to align by simply guess-ing the rotation of the adjustment knob or the accuracy of the componentsfor fixed filter values.

A passive bandpass filter has twice as many components as a passive highpass or low pass filter. For example, a second order (12 dB) bandpasscrossover has two inductors and two capacitors, which results in a second-order filter when the pass band begins and second order when it ends.

Speaker Types and EnclosuresSPEAKER TYPES Over the past 10 years, auto manufacturers have adopted fairly standardspeaker sizes. The most common are:

3.5” round (8.7cm)

4” round (10cm)

5.25” round (13 cm)

6.5” round (16 cm)

165mm Euro round (16.5cm)

4” x 6” oval

5” x 7” / 6” x 8” oval

6” x 9” oval

4” x 10” oval

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Mounting patterns are relatively standard, with the exception of the 6.5”speaker, which has always been tricky. Many so-called 6.5” aftermarketspeakers are actually a 6” (also called a 6” three-hole). This was a commonspeaker for pre-1996 Fords and some Asian imports, particularly Honda.Most modern American vehicles have a standard 6.5” or 6” x 8” speaker.The 6.5” three-hole speaker usually has a smaller cone (usually 5.25”) and a6” frame with a generous 1/4” mounting lip. The other size is a true 16.5 cmloudspeaker. This size has a true 6.5” cone and usually a much larger frame.Many European and Japanese vehicles take this size.

The standard “drop in” sizes are the 3.5”, 4” x 6”, 5” x 7” (commonlyreferred to as 5” x 7”/6” x 8”) and 4” x 10.” These speakers are usually usedto replace factory speakers and do not normally come with grills or mount-ing hardware. More and more often, OEM speakers have integrated framesthat are shaped as a unique module, specifically intended for the applicationinto which they are installed. Many Toyota, Chrysler, Mercedes Benz, Audiand Volkswagen vehicles follow this trend. To install an aftermarket speakerin place of an OEM speaker, you will need an adaptor in some cases. If no commercial adapter is available, you will have to fabricate a suitablemounting baffle.

There are many types of speakers. They can be classified by application or by type. Applications include woofer, midbass, mid-range and tweeter.Types include multi-elements (coaxial) or dual cone. Speakers packaged ascomponents are often two-way and three-way separate systems. Technically,subwoofers are even components because they are intended for use withother speakers to complete a full range audio system. With componentspeakers, each has a job and all work together to create a complete sound.

In a component system, a crossover is required either using passive compo-nents or an active crossover with discrete amplifier channels (meaning adedicated channel for each frequency range). An active crossover, thoughmore expensive, is the easiest to adjust and optimize for quality sound. Theadvantage of this system is frequency separation and overall superior soundquality, if designed properly. The different pre-assembled or pre-designedpassive crossover systems are the most widely used, especially where mid-range and tweeter component speakers are concerned. The passive crossovernetworks are optimized to work with the speakers as an entire system andare easy to install. Using a pre-designed passive crossover network alleviatesthe guesswork. Remember to keep the passive crossover networks away from potential sources of radiated noise when installing them!

SUBWOOFER ENCLOSURES TYPESOf all the aspects installers must consider for car audio system design andinstallation, designing and executing accurate low frequency reproduction isone of the most difficult. So many black magic tales surround this topic thattalking to two or three people can bring two or three different ideas aboutthe ideal low frequency reproduction techniques. The truth is that there isno one single perfect low frequency system.

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Component mid/tweeter

sets should be installed

relatively close together to

achieve the best hand-off

between speakers in the

range of the crossover.


Remember to keep

passive crossover networks

(especially large inductors)

away from any radiated noise

sources. This includes batter-

ies, alternator charging cables

and high current power and

ground distribution blocks.

It is not necessary to

mount a subwoofer near mid

and tweeter speakers to get a

good blend of sound. You can

mount subwoofers in many

places throughout the vehicle

with great results.

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Each type of low frequency system for the car has its own set of advantagesand disadvantages. Each system is well suited for some users and perhaps apoor choice for others. It all depends on what the customer expects. Thecustomer usually is not trained enough in low frequency reproduction tech-niques to walk and say something like “I need two 15’s and 1000 watts torun them.” The whole reason they are seeking professional service is becausethey really do not know what they need. That is where understanding thedetails of low frequency reproduction becomes essential for the ProfessionalMobile Electronics Installer.

Before you can spend time interpreting the user’s requirements into data, tryto find a language in which to do the conversing. No customer seems tohave a particular way of doing this, as you may have found out. Instead, youget terms like “I’d like more boom” or “tighter bass” or even “I want to hithard when I’m cruising.” That is simply not enough information to fill asound system design requirement-not yet anyway.

To begin building a “language” to talk about low frequency system design,you must look at the critical points that will be in nearly every situation youwill encounter. First, understand that it is not just the parameters discussedin this section that make the magic happen. It is also the way in which theyinteract with one another that sums up the performance of the final product.The points of particular interest include, but are not limited to:

Resonance - The resonant frequency of a low frequency system is the easiestnatural point of work, expressed in units of frequency. Resonance is themusical note that the low frequency system plays with the least amount ofeffort. Do not confuse this with the note that plays the loudest, becausethese are not always the same. Resonant frequencies are noted by abbrevia-tions in Hz. There are several low frequency systems with more than oneresonant point because of enclosure and port resonance.

Half Power or F3 - Half power is the point at which the low frequency system achieves a -3db down point in the attempt to extend into the lowestfrequencies the system is capable of (how low it will play). The point of reference for which the -3db down point is judged varies with the enclosuretype and calculation method. Half power, for some, is judged from the resonance point, while for others it is taken from the 0db reference after resonance has occurred. For now, just understand that half power is whenthe system begins to roll off. Since all low frequency systems are high-passor bandpass systems (regardless of additional protective filtering on the low side), the half power point is where the actual rate of attenuation of the low frequency system begins.

System Q - System Q is very similar to Q in the signal processor section.The Q of a low frequency system describes the shape of the response curvearound the resonance point(s). A flat, wide Q is referred to as a low Q, whilea peaked, narrow Q is referred to as a high Q. The lower the Q, the lower

Resonance-the easiest

natural point of work-is the

frequency (in Hz) at which the

object naturally resonates.

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Margin Notes


There is no single perfect

enclosure design. Each type

has inherent benefits and

drawbacks and should be

chosen based upon the

customer’s requirements,

vehicle and equipment

choices.

F3 is the point at which

the low frequency system

experiences a measurable and

continued reduction in power

handling as frequency

decreases. This is known as

the “roll off” of the enclosure.

Actual F3 values are typically

lower once the enclosure is

installed into a vehicle.

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the group delay of the low frequency system. Group delay is the frequencydependent variation in signal delivery time from the audio component orspeaker system.

Besides these three parameters, there are many more. Things like phaseangle, frequency response, maximum excursion (Xmax), impedanceboth at resonance and nominal points (Zmax and Z), impedance damping,out-of-vehicle response vs. in-vehicle response, power handling, efficiency,distortion and, of course, the installer’s own time and effort are all things to consider. The three parameters highlighted previously will predict severalof these things for you.

Building enclosed subwoofer systems helps the subwoofer to be more effec-tive at moving air. Moving air at low frequencies is how we create bass,whether in a car or in a room at home. The enclosure has a lot to do withthe phase of a low frequency system. It has a lot to do with cancellation.Without enclosures of some type, subwoofers are literally moving air againstthemselves. Enclosures trap the air on at least one side of the woofer (usuallythe back) and keep cancellation to a minimum, thereby allowing the sub-woofer to move large amounts of air without creating equal and oppositepressures to cancel itself. This section explains different types of low frequency systems that are common in mobile audio systems. While somemay seem simple, they also may be well suited to matching up with a particular design goal.

ENCLOSURE CONSTRUCTIONPlanning is the first step in constructing a great subwoofer enclosure. Everysubwoofer is designed to operate in a specific range of enclosure volumes.The recommended volume range for almost any brand of subwoofer is avail-able with the data sheet included with the woofer, on the manufacturer’swebsite, or by calling the manufacturer’s technical support department.Often, there are several slightly different recommended enclosures for eachsubwoofer, each one tailored to a different listener preference or application.There is no one magic enclosure volume or type, but rather a range of possibilities. No matter how well conceived, a subwoofer enclosure must besoundly constructed to realize its maximum potential. This portion of theMECP Advanced Level Study Guide covers the basic methods of constructing,bracing and sealing subwoofer enclosures.

Subwoofer enclosures are commonly constructed from medium densityfiberboard (MDF). MDF features low air permeability and high rigidity,while being easy to manipulate. Particleboard is less expensive, but shouldnever be used in the construction of a subwoofer enclosure. It is air perme-able and susceptible to chipping and cracking. Marine grade plywood is alsoa viable material, however it is slightly more difficult to manipulate thanMDF. In general, choose MDF in most applications because you can cut andsand it easily, buy it at nearly all wood supply outlets, and pay less comparedto other materials.

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Margin Notes


The “Q” of an enclosure

describes the concentration

of energies at one frequency

relative to other neighboring

frequencies.

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Fiberglass is the ultimate material from which to construct the enclosure. It is extremely rigid, completely air tight, and able to take on almost anyshape imaginable. You can increase rigidity by adding thickness and bychanging the shape to minimize the flat unsupported surfaces. Fiberglass ismuch stronger at a given thickness when it has a curve. Because the poly-ester-based resins used in fiberglass work are toxic, be sure to use properventilation, respirator and skin protection.

Composite construction is an advanced technique that can yield excellentenclosures. A composite is merely a combination of two different materials.A composite is stronger and better damped than a wall of the same thicknessconstructed from only one material. MDF glued to marine grade plywood isone example of a composite wall. A layer of fiberglass over MDF is anothercommon composite. In addition to the added rigidity and damping, theadhesive joining the layers further seals the surface of the enclosure. Whiletheir complexity adds extra time to the construction process, compositeenclosures offer amazing performance. MDF “rings” suspended withinstretched forming materials on custom enclosures are an example of usingcomposite construction to achieve unique shapes of a subwoofer enclosure.

Internally bracing the enclosure is vital to maximize the output of a sub-woofer. Enclosure wall flexing reduces the amount of pressure the sub-woofer can generate. As enclosure walls flex in unison with thesubwoofer(s), some of the acoustic energy is converted to mechanical energyand lost. Bracing adds extra rigidity to the enclosure wall at places where itflexes most. It is also necessary to use bracing or increased wall thicknesswhere MDF rings are suspended within stretched forming materials on cus-tom enclosures.

Placement of the brace is critical to its performance. The wall bows in andout as the subwoofer pressurizes the enclosure, with the greatest movementat center. In very large enclosures, wall motion can be radically increasedthrough the phenomenon known as coincidence. When the frequency beingplayed by the subwoofer has a wavelength identical to the length of theenclosure wall, a standing wave occurs. Additional standing waves occur for wavelengths that divide evenly into an enclosure wall dimension.Fortunately, they dissipate much less energy, and are mostly irrelevant.While the enclosure’s flexing behavior is daunting to describe, it is easy toeliminate.

Place braces at the one-third, one-half and two-thirds points on the wall toaddress the significant coincident bending modes. During the designprocess, remember to account for the volume of any braces. Building thicker,more rigid walls improves any design tremendously, but rigorous bracingbecomes increasingly vital as the enclosure size increases. While bracingadds a level of complexity to the construction of the enclosure, it pays off in sound quality and pressure. When in doubt, add more bracing!

Add additional bracing and

wall thickness to the area

where MDF rings are joined to

forming material in a custom

composite enclosure design.

This will help eliminate surface

material cracking due to

extreme wall pressures

inherent in many enclosures.

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Sealing the enclosure is the next step. Air leaks cause the speaker to behaveas though it were in a larger enclosure, adversely affecting its output andsound quality. All of the walls, braces and dividers must fit snugly if they areto seal properly. Therefore, cutting the pieces precisely is mandatory toachieve a tight seal. An adhesive such as silicone caulking can fill any tinygaps that may exist between the walls. Be certain to allow adequate time forthe glue to dry before testing the enclosure. Avoid using a flammable adhe-sive such as Liquid Nails for sealing purposes. Such an adhesive may causean explosion if not completely dry while a woofer with a vented voice coil isinstalled and driven to high excursion (potentially sparking the voice coiland igniting the residual fumes).

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Although difficult to tell,

MDF is a leaky material.

For optimum results, seal

the inside cavity with

polyester resin, sealer paints

or rubberized undercoating.

The greater the woofer

excursion, the greater

the leak experienced in

the untreated MDF.


Figure 132. Speaker Enclosure Construction

Though they are too tiny to see, millions of microscopic gaps in mediumdensity fiberboard allow air to pass through. To stop that flow of air, theentire inner surface of the enclosure should be coated with a sealant such asfiberglass resin. It is also possible to treat the interior of the enclosure withrubberized undercoating. Make certain to cover the entire surface evenly,and allow adequate curing time before installing the subwoofers.

The subwoofer must form a tight seal with the enclosure to prevent air fromleaking under the mounting flange. At high volume, it is easy to check forair escaping around the edge of the subwoofer. You can fix leaks with adhe-sive foam gasket tape. Silicone caulking can also be used, but makes the subwoofer difficult to remove. When possible, use the adhesive foam gasketinstead of silicone or other sealants dispensed from a tube.

Covering the enclosure is the final phase. Carpet, vinyl and laminate are the most commonly used materials on MDF enclosures. With fiberglassenclosures, many installers are able to paint the enclosure with a catalyzedprimer, followed by epoxy primer, and then normal automotive paint tomatch the paint on the vehicle. Whatever material you choose, use a straightedge to trim vinyl and carpeting precisely and be certain to do any spray

14683_CEA 2/10/04 6:37 PM Page 196

primer and paint in an OSHA-approved ventilated location. When using carpet, gently tapping along the seams with a mallet makes them much less visible. Take time to finish the appearance of the enclosure carefully, so that its appearance will reflect its outstanding performance.

Subwoofers totally depend on their enclosure to produce good sound. No matter how well it is engineered or how “pretty” it looks, a subwooferrequires a carefully constructed enclosure to achieve its maximum perform-ance. A little extra time and effort during the construction process can makethe difference between sounding good and sounding great. Often the bestsounding enclosures do not have the prettiest interiors. Bracing and variousvibration treatments can leave the inside looking less that show quality, yetthe sound benefits are unmistakable. Remember that neon lighting and clearacrylic viewing windows will not make an enclosure sound good if it is notconstructed correctly. Plan ahead and take the time to build it right!

THE IDEAL SUBWOOFER ENCLOSURE?It seems like everyone who listens to or installs mobile audio systems has an opinion about which type of enclosure is the best one. Who is right? Inracing the saying exists, “What wins on Sunday, sells on Monday.” In caraudio, what does well in sound quality (SQ) or sound pressure level (SPL)contests will do well on the sales floor. So, what kinds of boxes win in thecontests? Is there one enclosure that always wins? The answer is NO. If oneenclosure was truly superior in every way, that would be the only enclosureinstallers used, but that is not the case.

Mobile audio systems use sealed boxes, ported boxes and bandpass boxes.Each type has inherent advantages and disadvantages. Throughout this section you will see that there is no “magic box” that does everything well.Rather, each type will have a compromise in one or more areas. Each enclo-sure type is referred to by its mechanical (moving parts) orientation with theairspace rather than the acoustic and/or electrical order it exhibits. This isdone to avoid confusion, because what is one person’s second order is another person’s third or fourth order-depending on the crossover used. The enclosures in this section simply relate to the woofer and the box.

The key to proper enclosure design is deciding which factors are importantfor the system that you are working on and selecting a subwoofer that willperform well in that type of enclosure. Remember that all subwoofers do notnecessarily work in all enclosure types.

INFINITE BAFFLE DESIGNSInfinite baffle designs (sometimes referred to as free-air) technically are justvery large sealed enclosures. As the size of the box changes, certain inherenttrade-offs become evident. Each type of box in the “sealed” category of lowfrequency enclosure designs has its advantages and disadvantages.

A speaker in an infinite baffle relies solely on its suspension for the restoringforce required to return the cone to rest and to protect the speaker from over

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Figure 133. Infinite BaffleDesign (also called “Free-Air”)

"Free Air"

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excursion. The resulting sound is determined entirely by the speaker’sparameters, and there is no acoustic way to alter it during installationbecause there is essentially no box-just a baffle. A speaker created for infinitebaffle application must be carefully designed for optimum performance inthat application. It will typically handle less power than an acoustic suspen-sion driver and is more susceptible to over excursion when driven hardbelow the resonant frequency of the driver (Fs).

In fully enclosed sealed enclosure designs, the air inside the box supplies apart of the restoring force, as well as protecting the woofer(s) from overexcursion. The resulting sound can be changed by adjusting the enclosurevolume, either by increasing or decreasing the actual size.

A theoretical infinite baffle would extend in infinite dimensions to absolutelyisolate a speaker’s front airwaves from its rear airwaves. In reality, an infinitebaffle does have limiting dimensions, although it still appears to be infiniterelative to the speaker.

The idea is that the longer the baffle, the longer the path for the airwaves totravel before they can mingle and interfere with each other. In other words,to hear bass to a desired low frequency, the infinite baffle dimensions mustbe greater than half the wavelength of the lowest reproduced sound. Forexample, assuming a woofer can reproduce a 20 Hz tone, its infinite bafflewould have be greater than 28.3 feet in either direction to keep the front and rear airwaves from canceling each other.

In mobile applications, “real” infinite baffles are much too large, so we mayuse a door or a rear deck as an infinite baffle with the enclosed trunk spaceacting as the enclosure. In these applications the infinite baffle is nothingmore than a large, sealed enclosure where the size of the trunk has littleeffect on the woofer’s low frequency response. Smaller trunks, for example,may sound different if loaded up with groceries or golf clubs because theapparent volume of the trunk changes.

A common misconception is that infinite baffle applications are easier tobuild and less expensive than sealed or vented enclosures. This is absolutelynot true. In mobile audio applications, it is imperative that the front wave becompletely isolated from the back wave of the speaker. For this reason, rigidbaffles must be installed under the package tray and behind the rear seat.Remember that an infinite baffle in a car is really a just a big sealed enclo-sure and any leak between the trunk and interior will result in a loss ofsound output.

Any surface that vibrates between the trunk and the interior will transferenergy from back to front waves, causing cancellation. This vibration ormovement of vehicle components is completely useless as a means of pro-ducing bass. In other words, any time you see a vehicle driving by with alicense plate vibrating, body panels buzzing, or trunk lid vibrating, youimmediately know that the SPL inside the vehicle could be much higher

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Margin Notes


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if these vibrations could be eliminated. As a result, a well-designed infinite baffle will often cost as much as constructing an enclosure and take at leastas much time to construct, if not more. As you can see, a good infinite bafflelow frequency system involves much more than cutting a hole and mountinga speaker.

The main advantage of an infinite baffle application in a car is no loss oftrunk space. However, the disadvantage is that this type of enclosure cannotbe acoustically tuned to adjust the system frequency response or the powerhandling. If the customer wants more flexibility in sound contouring, youwill need to look at other enclosure types, such as sealed, vented or band-pass designs.

Infinite baffle systems exhibit approximately ±6dB (1st order) per octave of roll-off if not otherwise filtered or coupled to resistive damping material.This type of infinite baffle system can-depending on the driver power han-dling and the system “Q”-have medium to low power handling if no addi-tional filtering is used.

Benefits of infinite baffle Designs - Saves trunk space. Good low tomedium output. Generally good sound quality.

Drawbacks of infinite baffle Designs - Low power handling. Low bassresponse. Not possible in a hatchback, truck, etc. Typically as muchlabor, if not more, than constructing a sealed enclosure.

SEMI-CLOSED APERIODIC DESIGNSA speaker becomes aperiodically damped when it is required to pass its energy through a resistively leaky material. In this way an infinite baffle subwoofer that fires through the back seat of a sedan or coupe will oftenprovide the benefits of an aperiodic system. The seat material is a crude buteffective form of aperiodic damping, allowing the speaker to perform betterthan if it had been installed firing up through the rear deck if the enclosed spaceof the trunk is unusually large. Unobstructed mounting is good for pressuretransfer into the passenger listening area, but large enclosed trunk spaces of20 or more cubic feet may provide limited power handling and an erroneousfrequency response. Putting a speaker in an enclosure adds resistance to thespeaker cone movement, but the resistance can still improve with a calculateddensity of “leaky” enclosure materials.

In a semi-closed periodic system, the installer places a resistively leaky material on the back of a subwoofer that fires through the unobstructed reardeck. In this case, the aperiodic material is held in place by a box-shapedframework surrounding the rear speaker. Aperiodic applications have usedsimple fiberglass insulation (as used in many attics), Dacron, and polyesterpillow stuffing. The importance is the relative density for a given thickness.The denser the material, the more slowly air passes out of the leaky semi-enclosed subwoofer cavity to neighboring air spaces. The amount of conemovement (or pressure) created by the subwoofer influences the resistivityof the air leak.

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Margin Notes


Figure 134. Semi-ClosedAperiodic Design

HighPressure

Inside

LowPressureOutside

14683_CEA 2/10/04 6:38 PM Page 199

Some have commented that an aperiodic enclosure for a subwoofer is verysmall, when in fact, the enclosure is not a complete enclosure at all; it issimply a support for the resistively leaky damping material. This system istechnically still an infinite baffle system, with an aperiodic damper on theback of the speaker. It is for this reason that a small, semi-closed aperiodicsystem will not function in a hatchback.

Aperiodic designs are still used in some SQ competition mobile audio sys-tems as well as in certain home audio speaker designs. The vast majority ofconsumers looking for “bang for the buck” would find that a sealed or vent-ed enclosure design gives better results. Sound quality aficionados may findthe semi-closed aperiodic designs to be an ideal compromise between aninfinite baffle design and the control of an infinitely variable sealed enclosure.

Benefits of Aperiodic Designs - Improved power handling and efficien-cy over an infinite baffle design. Improved bass response. Easy to buildand tune with inexpensive test equipment.

Drawbacks of Aperiodic Designs - Causes F3 point to rise slightly,trading off a small amount of low bass loss for an improvement in over-all performance. Can be counteracted by using larger woofers and moreamplifier power in many cases.

SEALED ENCLOSURE DESIGNSThe sealed box is also referred to as air-suspension or acoustic-suspension.With the possible exception of some infinite baffle designs, the sealed box is the easiest to design and build, which makes this a good all around designif the subwoofer is suited for a sealed enclosure environment.

The sealed enclosure design earned a patent in 1949 for Harry Olson, theman who worked out the design details. In 1954, a company known asAcoustic Research made this design very popular, in part because of its size. Sealed enclosures are typically much smaller than the other designs.Back in the 1950s, this was especially nice as the age of bookshelf speakerswas born!

The idea behind a sealed enclosure design is that the air trapped inside thebox will work to assist the speaker’s suspension, which gives us the term air-suspension. As the speaker moves outward, the air behind it is pulledwith it, creating a decrease in pressure inside the box. This acts like a vacu-um and pulls the speaker back inward. Similarly, when the speaker movesin, the air that is compressed pushes out on the speaker. Logically, the morethe speaker moves in or out, the greater these forces are. If the speaker weredesigned with a loose suspension and a long excursion, the sealed enclosurewould provide smooth bass response, since the stiffer air pressure within the enclosure would control speaker excursions.

The performance of a sealed box is a result of the relationship of the speaker’s parameters and the volume of the box. In 1972, Richard Small

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Margin Notes


"AcousticSuspension"

Figure 135. Sealed EnclosureDesign (also called AcousticSuspension)

14683_CEA 2/10/04 6:38 PM Page 200

(of Thiele-Small fame) published the most definitive work to date on sealedenclosure design. Most of what we know about predicting the performance ofsealed enclosures is based upon his work. When calculating the ideal sealed enclosure volume (Vb), you are in fact calculating for the correct vacuum and pressure for that particular speaker.

Sealed enclosures are known for their “tight” sound. A properly designedsealed box can have excellent transient response characteristics. The upperend of a sealed box’s response is relatively unaffected by the enclosure itself,allowing for excellent midbass transition as well.

The amount of low frequency content of sealed enclosures can vary based on box size. The volume of air trapped in the enclosure controls how freelythe speaker can move. Sealed enclosure designs tend to exhibit roll-off ±12 dB (2nd order) per octave depending on the ratio of the physical size of the environment (Vb) versus the driver compliance (Vas). By making theenclosure smaller, the air spring is tighter (higher Qtc), and the cone travelis more controlled. This will limit low frequency excursion problems, butsmall boxes can also limit low frequencies altogether.

Very low Q sealed enclosure systems (.45 and lower) exhibit roll-offs onlyslightly different from that of infinite baffle designs, making them a highconsumer of available space without much increase in frequency response orpower handling of an infinite baffle system. Basically, making the enclosurelarger decreases the air spring in the box. This allows the speaker to movemore freely (lower Qtc). This also allows the speaker to play lower frequen-cies more effectively. By enlarging the enclosure too much, however, thespeaker can more easily move beyond its excursion (Xmax) limit, openingthe door to distortion and possible mechanical problems.

These changes in enclosure size will affect how smooth the frequencyresponse is in the lower frequencies. In general, at frequencies below 30Hz,sealed boxes will exhibit very good control over the speaker’s motion,improving mechanical power handling and reducing distortion. Between 30 and 80Hz, sealed boxes typically have a slight “knee” in their excursion.If additional power were used, this would be the first area to exceed the lin-ear excursion limits of the speaker, which results in higher distortion. Thishigher excursion can put a lot of stress on the speaker’s suspension as well.

If you are not sure how to judge which environment a driver prefers, usethese hints:

Find the efficiency bandwidth product (EBP) of the driver.

EBP = Fs / Qes

(This information should be on the speaker specification sheet or is available from the manufacturer.)

Numbers below 90 indicate a sealed enclosure design is acceptable, whilenumbers of 50 and below mean a sealed enclosure design is preferred.

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Perhaps the biggest drawback to sealed enclosures has to do with efficiency.For a given speaker in a sealed enclosure, efficiency will decrease with asmaller box size. As the box size increases, the low frequency outputincreases while the upper frequency output decreases. As the box gets smaller, the low frequency output decreases but a peak is created in theupper end. If you average the output at every frequency from 10 Hz to 100Hz, the larger box would have a higher overall output.

Keep in mind that a speaker in a large box does not handle power as well asit would in a smaller enclosure. If you are interested in creating a strongpeak in the upper frequency range for an SPL system, the output gain atthose frequencies combined with the improved power handling of the smaller box can be a benefit.

Speakers that share an enclosure baffle in a sealed enclosure are called“acoustically coupled.” This basically means that their acoustic output iscombined to create more output than each working on its own. The mostcommon acoustic-coupled enclosure is simply two identical woofers in onebox. Ideally, the enclosure would have a divider between the woofers to keep the airspace separate for each woofer.

If installing a divider is not practical or possible, multiple woofers can stillshare the same airspace. When sharing airspace, calculate the overall boxvolume as the optimum volume for a single woofer multiplied by the num-ber of woofers to be used. For example, if you calculate that one 10-inchwoofer requires a 0.75 cubic foot box, two woofers (same make, model,nominal impedance, etc.) will need 1.5 cubic feet, three will need 2.25 cubic feet and so on.

Some people contend that since the woofers actually share each other’s airspace, the overall box volume can be made smaller than the sum of twoseparate acoustic suspension boxes. This is absolutely not true. While thewoofers do share the box’s interior, there is no real benefit to this type ofenclosure design over a box with a divider. The woofers will interact withthe air inside the box according to their relative distances from each otherand interior walls.

At higher frequencies, standing waves may form pockets of irregular airpressure around the cones, thus causing them to deform and produce distor-tion. This effect will be greater in very small boxes where there is a lot ofcone excursion due to high amplifier power. Using a divider to isolate eachindividual woofer is ideal whenever possible. The divider also adds the benefit of interior bracing to solidify the speaker baffle and enclosure walls. If constructing an irregularly shaped box using fiberglass, make sure that thewalls are thick enough to prevent flexing, or add an interior brace and affixit to the walls with more fiberglass.

When a sealed enclosure with one or several subwoofers reproduces sound,the air inside the sealed enclosure actually increases in temperature. This in

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turn makes the air spring stiffer. If you fill the airspace with a fiber stuffing,the material will not only help dissipate the heat, it will make the systemwork as though it is in a larger box for decreased F3 and Qtc. Using thistechnique, you have an easy way to increase the apparent volume of the box without having to actually build a new one. Depending on the stuffingdensity (and the size of the enclosure), you can increase performance up to36 percent. Stuffing a poorly designed enclosure, however, will not make itinto a well-designed one. Think of stuffing an enclosure as fine-tuning it.

Three types of stuffing are in use today: fiberglass insulation, long-fiber wooland polyester fiberfill. Standard polyester fiberfill is recommended since it is easy to use, easy to find and inexpensive. Standard polyester fiberfill isavailable at any craft or fabric store. Interior suppliers use a polyester fillsold in rolls called Dacron. If your enclosure design specifies 50 percent fill,line all interior walls of the box (except the baffle) with 1-inch thick stuffingmaterial such as Dacron. If your enclosure design specifies 100 percent fill,loosely stuff the box with bulk fiberfill.

After all the homework has been done, sealed enclosure designs can be theeasiest to actually construct Good construction techniques are relatively easyto perform, even for an amateur.

Note that changes will occur when a speaker enclosure is fired into anotherenclosure (the car) and that change will differ depending on the physicalsize of the car interior or trunk and loading method (unaffected path,bouncing off rear window, facing into rear seat, etc.) This “boundary effect”is caused by the transfer function of the car, and is true with any speakersystem in a vehicle. (See the “transfer function” section in this chapter formore information.)

Benefits of Sealed Enclosure Designs - Box volume is small in comparison to other enclosure types. Good output for all music types.Easy to build and tolerant of small errors in design. Many well built pre-fabricated sealed enclosures available that offer good results.

Drawbacks of Sealed Enclosure Designs - Poor response below 30Hz when compared with a vented enclosure. Low-end response getsworse as enclosure size decreases. Typically requires more power for agiven output when compared to a vented or bandpass type enclosure.

VENTED ENCLOSURE DESIGNSThe vented enclosure’s beginnings can be traced back to acoustic work doneby Hermann Ludwig Ferdinand von Helmholtz, a late 19th century Germanphysicist. By altering the size of a tuning hole, Helmholtz discovered hecould construct an acoustic resonator that would tune to a unique pitch. You can hear this principle at work by simply blowing air across the openingof a filled soda bottle. In this case the tuning hole is fixed, but you canchange the length of the resonator by taking a drink. Blowing air again, youwill hear a lower pitch. If you could alter the size of the opening or use adifferent size bottle altogether, the pitch would also change.

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"Ported" or"Bass Reflex"

Figure 136. Vented EnclosureDesign (also called “Ported” or“Bass Reflex”)

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Early loudspeaker designers around the 1930s used the vented enclosureprinciple when they coupled the mechanically resonant speaker to theacoustically resonant box to create the bass reflex. Here the acoustic reso-nance was combined with the mechanical resonance to further extend aspeaker’s bass response and, at the same time, reduce cone excursion forlower distortion. However, the resulting sound was “boomy” and reproducedvoices that sounded muffled. Vented enclosures have actually been aroundlonger than sealed enclosure designs. A.C. Thuras received the originalpatent describing driver and vent interaction.

While several people throughout the 1950s did extensive work on the math-ematical models for ported boxes, it wasn’t until the late 1960s that acousti-cians and engineers fully understood the interacting dynamics involved increating a successful vented design. A.N. Thiele did perhaps the most com-prehensive and detailed work on the relationship of the speaker and vent inan enclosed air space.

Vented enclosures are also known as ported enclosures and bass-reflexenclosures. The basic idea behind a vented enclosure is to take advantage ofthe rear wave energy of the speaker. In a sealed box, the energy from the rearof the speaker is used to restore it to its original center (rest) location. Inported boxes, this energy is coupled with the energy from the front of thespeaker. When using a port or a vent, the column of air that is created bythe port has a certain resonant characteristic that will determine the tuningfrequency. By changing the size of the opening, the length of the port, or thevolume of the enclosure, you will change the resonant characteristic as wellas the tuning frequency.

Passive radiator enclosure designs can be thought of as a vent or port substi-tute. Rather than a tuned vent, an auxiliary drone diaphragm is used inplace. These systems have performance characteristics similar to a ventedenclosure. The passive radiator device looks like a cone or flat shaped speak-er without a voice coil or magnet assembly. The pressure inside the boxforces the passive radiator to move back and forth in tandem with the speak-er’s motion, like the air inside the port in a vented enclosure. Ideally, thisradiator should have a high compliance. You can tune these enclosures byvarying the mass of the passive radiator’s diaphragm. Greater mass equals alower tuning frequency.

Vented enclosures are more complicated to analyze than sealed enclosures.There is a delicate relationship between the enclosure size (box volume),port size (both the opening and length) and the speaker’s parameters. Bychanging any one of those parameters, you will alter the performance of thesubwoofer system. One of the possible advantages of a ported box over asealed box is output. For a given box size, a ported box will have additionaloutput capabilities over most of the usable sub bass range. This additionaloutput is compliments of the port. Essentially the port only has usable out-put over a very narrow range of frequencies. At the center of those frequen-

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cies, the speaker’s output and the port’s output are in relative phase witheach other. When two sound sources-like the port and speaker-are in phasewith each other, they combine to give you that additional output. When youplay frequencies below the tuning frequency of the box, the combined out-put from both the port and speaker begins to drop rapidly, causing a sharperroll-off than the sealed box. This is because their output is out of phase witheach other. The roll-off from a vented enclosure design is around 24 dB peroctave, compared to around 12 dB per octave for a sealed enclosure design.

Physically, a port can be PVC pipe, ABS plastic tubing or even a thick card-board tube. A port can also be a square duct or any other shape so long asyou follow the general rule of vent diameter. The recommended minimumvent diameter is typically one third of the cone diameter. Choosing too smalla diameter can result in a whistling sound known as vent noise. Additionally,at high power levels when a lot of air is moving through the port, the fric-tion between the air and the port’s walls diminishes the port’s ability to passair. At this point, the resonance frequency of the box is actually reduced,and the vented box operates more like a sealed box. This happens graduallyas the box plays lower, below its vent and speaker resonant frequency (Fb).Large ports are great, but there is also the practicality consideration of get-ting the large port into the enclosure. As you increase a given diameter, theport must be longer to maintain the same resonant frequency (Fb).

If you change the enclosure size and keep the vent tuning frequency (Fb)the same, the port size will still have to change. However, because of theinverse size relationship between the enclosure and the port, using thismethod to tune very small boxes can become quite difficult. For example, to achieve a tuning frequency of 35 Hz, a one cubic-foot enclosure wouldrequire a 3-inch diameter port that is 10.4 inches long. If you decrease thesize to 0.5 cubic feet and keep the port diameter the same, you would haveto increase the port length to 23.3 inches to keep the same tuning frequency.

To make matters even more difficult, the volume of air inside the port can-not be considered as enclosure volume, so you must subtract it from the volume of the box. For the 0.5 cubic-foot box, the port volume is 0.1 cubicfeet, and subtracting it from the box volume leaves only 0.4 cubic feet, result-ing in a revised tuning frequency of 40 Hz. To keep the tuning frequency at35 Hz, you must increase the box size to 0.6 cubic feet, which may be possible if there is extra space in the car. Constructing a vented box is notjust making a sealed enclosure and cutting a hole in it if it does not soundgood. A good installer must consider many design parameters.

If you are not sure how to judge which environment a driver prefers, usethese hints.

Find the efficiency bandwidth product (EBP) of the driver.

EBP = Fs / Qes

(This information should be located on the speaker specification sheet or is available from the manufacturer.)

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Numbers above 50 indicate a vented enclosure design is acceptable, whilenumbers of 90 and above mean a vented enclosure design is preferred.

When the vented enclosure reaches the F3 point, it has fallen 3dB in outputfrom other relative upper frequencies. This is usually near the vent/speaker/enclosure resonance (Fb), depending on the actual alignment used. Ripplerather than Qtc describes the shape of the response curve around and at thetuned frequency. Ripple is expressed in dB (either + or -) and represents theamount of increase or decrease in amplitude from the 0dB level of reference(flat response). Ripple values can be applied in these guidelines:

-2.5 to 0dB = an audiophile listener

0 to +2.5 dB = a normal or variety listener

2.5 to 3 dB = an extended bass listener

3.5 + dB = Boom freaks, cruisers and dB monsters

A ripple of -2 to +2 will maintain the best transient response and accuracy;most listeners can only hear an increase or decrease of 3dB or more.

Power handling below Fb is poor since the air inside the vent no longerpushes against the woofer and thus allows it to easily exceed maximumexcursion. To avoid this distortion-producing artifact, add active subsonicfiltering to the audio chain feeding the amplifier that powers the ventedenclosure. Use an active 12 or 18 dB per octave high-pass filter, with the cut-off frequency set slightly below F3, to eliminate the danger of over excur-sion. Many signal processors and application-specific subwoofer amplifiersfeature subsonic filtering.

Benefits of Vented Enclosure Designs - Usually have lower bassresponse than a sealed enclosure. Great power handling above the F3point.

Drawbacks of Vented Enclosure Designs - More complicated to build.Less tolerant of errors in design or construction. Easy to damage thewoofer with excessive “bass boost” below Fb unless you use a subsonicfilter.

BANDPASS ENCLOSURE CHARACTERISTICSBandpass boxes experienced a huge wave of popularity in car audio a few years back. Many people will be surprised to know that they have actually been around for quite a long time. The first patent for a bandpassenclosure was issued to Andre d’Alton in 1934. Since then, and especiallyover the past 10 to 15 years, the industry has made significant strides indefining and predicting the way they work. Many companies are now usingbandpass enclosures as part of a home subwoofer/satellite setup. Designsfrom companies like Bose, KEF and Acoustic Research have become quitepopular in home audio.

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Tuning a bandpass enclosure involves changing conventional enclosuredesign mentality-and that requires enclosure design software to efficientlypredict the outcome. Many car audio manufacturers have taken the liberty of offering computer-aided bandpass enclosure designs to their customersand dealers.

The term bandpass comes from a rather unique characteristic of these enclosures. In addition to affecting the low frequency of the speaker, theseenclosures affect the higher frequencies as well. Bandpass enclosures are usu-ally constructed with dual chambers and share the following design criteria:

A bandpass enclosure has a woofer in a sealed or vented primarychamber that fires into a secondary vented chamber. The woofer in abandpass enclosure is enclosed on both sides.

The secondary chamber acts like a high-frequency attenuator oracoustic low-pass filter with a 12 dB per octave roll-off.

For a single reflex bandpass enclosure, the low frequencies follow asecond-order network response, rolling off at approximately 12 dB peroctave, depending on the bandwidth of the response.

For a dual reflex enclosure, the low frequencies follow a fourth-ordernetwork response, rolling off at approximately 24 dB per octave,depending on the bandwidth of the response.

Bandpass designs essentially only allow a certain band of frequencies to passthrough the enclosure. In bandpass enclosures, the woofer no longer playsdirectly into the listening area. Instead, a port or ports channel all of the output into the listening area.

SINGLE REFLEX BANDPASS DESIGNSWith the single reflex bandpass enclosure, the speaker is mounted in asealed chamber and fires into a ported chamber. By altering the size of thechambers, and the area and length of the port, you can alter the speaker’sperformance. The interaction between the two chambers and the port is veryinvolved. The sealed section will determine the low frequency limit of thesystem while the ported side determines the amount of gain or loss and theshape of the response. The port needs to be tuned to the resonant frequencyof the sealed box to ensure a centered, symmetric response shape.

Single reflex bandpass designs are often called fourth or fifth order enclo-sures because of their roll-off characteristics. They exhibit about +/- 12 dBper octave (second order) on the low end (high pass side) and another +/-12 dB per octave (second order) on the high end (low pass side), which ishow the fourth order term evolved. Putting a first order crossover in serieswith the enclosure increases the electrical roll-off by another order, hencethe term fifth order. In either case, variables make the “order” different eachtime, which is why you should become familiar with the term single reflexbandpass.

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Fourth Order

Figure 137. Single ReflexBandpass Enclosure Design (alsocalled “Fourth Order”)

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Single reflex bandpass enclosures exhibit some extremely attractive attrib-utes for the average consumer. While maintaining a relatively small enclo-sure size, this low frequency system has excellent low frequency and effi-ciency. In other words, it plays real low and real loud. No wonder this is apopular enclosure design.

These enclosures also have the ability to mask the problem areas of a partic-ular driver. While this is good in some cases, it usually ends up being badoverall. Often the listener cannot hear the speaker destroying itself-when infact, it actually is. Turning up the bass knob or sliding up the bass EQ is avery real example of how bandpass systems can be harmed without everreally knowing it until it is too late. As with the vented enclosure designs,the single reflex bandpass system is unforgiving of errors in its design.Exceeding tolerances of even 10 percent can be fatal in the long run, and-inthe short run-sound bad.

Although the single reflex bandpass system does not need a crossover, it is agood idea to limit the signal fed into the system with a filter. Filtering thesignal reduces resonant harmonics from the vented chamber of the box(sometimes called pipe organ resonance), which will ultimately color themid-range frequencies in the system.

Benefits of the Single Reflex Bandpass Enclosure Design - Great bassfrom reasonable sized enclosures. Single driver systems work well toreduce costs. A lot of “bang for the buck.”

Drawbacks of the Single Reflex Bandpass Enclosure Design - Muchharder to build. Speaker distortion is difficult to hear and damage to thespeaker can easily occur without notice.

DUAL REFLEX BANDPASS DESIGNThese enclosures are similar to a single reflex bandpass except that bothchambers are vented. This has the benefits of the vented side for the lowpass acoustic filter (front chamber) as well as the boost in the low end fromthe vented rear chamber.

Note that with the dual reflex bandpass design, the driver mounted insidehas no connection to the outside listening area. The driver is merely a pistoncausing the two vents to produce sound in much the same way that a speak-er does. It does not matter if the driver mounts with its cone facing out orin. It is important to note that the two vented cabinets are 180° out of polar-ity from each other. Vents must be tuned at least an octave apart to reducecancellation.

Dual-reflex bandpass low frequency systems generally exhibit a roll-off ofabout 18-24 dB per octave on the high pass and 12 dB per octave on the lowpass. This enclosure is often called a sixth order box because of its acousticalcharacteristics. The term dual reflex bandpass provides a more accuratedescription, since the orders of this system will vary when active or passivecrossovers are incorporated.

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"Sixth Order"

Figure 138. Dual ReflexBandpass Enclosure Design (also called “Sixth Order”)

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Dual-reflex bandpass systems are very “bass heavy,” especially near thetuned frequencies. This may be a good choice for a listener who places ahigh value on tremendous amounts of low frequency in the playback of theirmusic. For the audiophile, this type of enclosure may just be too much ofone thing and not enough of the other, creating an imbalance in what thecustomer would consider ideal.

As with any type of low frequency system, loading it into the cabin of avehicle changes its low end drastically. This effect that the vehicle has on the response is called transfer function. Be sure to factor transfer functioninto your design, otherwise you may end up with more bass than you willever be able to use. Computer design programs usually allow curve overlaysto simulate this, which is just another good reason to use software in designing these.

As with single reflex bandpass systems, dual reflex bandpass systems havethe ability to mask the problem areas of a particular driver. While this isgood in some cases, often the listener cannot hear the speaker destroyingitself-when in fact it actually is. In dual reflex bandpass designs, exceedingtolerances of even 10 percent can be fatal. Again, computer simulation isrecommended to save you from errors.

Although dual reflex bandpass designs exhibit a bandpass acousticalresponse, you should limit the signal fed into the system by using a filter.This reduces resonant harmonics from the vented chamber of the box, whichwill ultimately color the mid-range frequencies in the system. These systemswill also benefit from a high pass filter that will limit musical informationbelow the F3 (-3 dB down point). Information below the F3 can cause seri-ous excursion and power handling problems. Remember that the maskingeffect of the bandpass system hides these problems until it is too late.

Benefits of the Dual Reflex Bandpass Enclosure Design - Amazingbass from even small drivers.

Drawbacks of the Dual Reflex Bandpass Enclosure Design - Verydifficult to design and build correctly. Not as good in accurate soundquality because of the many vents sound must travel through.

THE BASIC DIFFERENCES BETWEEN SINGLE AND DUAL REFLEX DESIGNSThe differences between single reflex and dual reflex bandpass boxes aresimilar to the differences between sealed and ported boxes. Single reflexboxes, with their sealed rear section, have better transient response, bettercontrol in the extreme low frequency range and less efficiency. Dual reflexboxes have higher output capability, and are typically larger in size for simi-lar low frequency extension. This should show you how flexible bandpassboxes can be. You have the option of shifting the response curve higher orlower in frequency, up or down in amplitude, and as wide or narrow as youneed. With all those variables come complications.

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Bandpass boxes are very complicated to design and build. Single-reflex band-pass designs are the easier than dual reflex bandpass designs, yet both typesare still considered tricky. Making a mistake with a bandpass box can havedramatic results on enclosure performance, usually for the worse.

In either type of bandpass enclosure, a speaker can literally distort itself todeath-and listeners could hardly tell it from the front seat of the car. Avoidexcessive bass-boosting opportunities in the signal chain because additionaldamaging distortion may go unnoticed until one day, the speaker simplyquits working.

Single reflex bandpass enclosure designs do not require a subsonic filterbecause of the sealed chamber shallow roll-off. Use active (preamp level)subsonic filtering on the amplifier powering a dual reflex bandpass enclo-sure. Be sure to specify an active 12 or 18 dB per octave high-pass filter(with the cutoff frequency set slightly below F3) to eliminate the danger ofover excursion.

Sound in the VehicleLOW FREQUENCY TRANSFER FUNCTION Anyone who has experienced a dramatic increase in the bass output of a lowfrequency system when it was loaded into the car from the shop floor has gotthe basic idea of the transfer function concept. The phenomenon is not new;it has been around as long as sound itself. Transfer function is simply theoverall effect that the environment has on the frequency response and ampli-tudes of a sound pattern. While transfer function mostly involves increases inlow frequencies when we apply it to car audio, there are also times whendecreases in output occur and/or frequency responses overlap or have widegaps. This is all a part of complex sounds bouncing around in an automobileenvironment. Low frequency systems are the most radically affected.

Years ago, many car audio experts began to faithfully use special computersoftware to help design and predict the response of speaker box applications.This was a tremendous timesaver, with almost guaranteed results. Computerdesigns were-and still are-very useful. What most installers and systemdesigners never bothered to note was that the computer-generated designwas not taking into account any other space but imaginary infinite freespace. The computer did not account for reflections, absorption or bound-aries within the usable frequency range of the speaker. That type of space iscalled an anechoic space and the chance of finding an anechoic environmentin a mobile application is just about impossible.

So installers live with the very real fact that the sound from a speakerchanges as you put it in different rooms, car interiors and speaker enclo-sures. With this in mind, would it not make sense to add that analysis to oursophisticated computer-generated designs? You bet it would! Although itcould never compensate for the passenger/cargo load and other random vari-ables, predicting the transfer function with some reasonable accuracy couldpaint a clearer picture of the final outcome.

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Sealed Enclosure (Out of Car)

Vented Enclosure (Out of Car)

Sealed Enclosure (In Car)

Vented Enclosure (In Car)

Figure 139. Low FrequencyTransfer Function Examples

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Transfer function measurement, or mapping, involves exactly that, addingthe vehicle effect to the overall design of a low frequency system. Doing thismeans you can come much closer to a very accurate sound in a car than youcould have by simply guessing or ignoring it all together. If someone hasnever had bass in his vehicle, the idea that “it just gets louder” when youload a speaker box into the vehicle sounds like a novel idea, certainlyappealing at car shows and cruise nights. However after a while, listeningfatigue sets in, and the beautiful music and pleasant drive soon are not sobeautiful and pleasant anymore.

Automobile manufacturers certainly take transfer function into accountwhen implementing an OEM system design into new vehicles, so shouldMECP certified installers be doing it too? If you already use computer enclo-sure design software, it may be easier than you think. If you do businesswith consumers who do not install, here’s a great reason to encourage themto work only with a trained professional car audio installer. The results forthe customer will be well worth the effort, especially since money does notgrow on trees and they should be able to enjoy their music for more than 15minutes without extreme listening fatigue. Believe that it is possible!

Although everyone will prefer a different sound, a good finished mobileaudio system should always have good balance from frequency to frequency,including midbass, mid-range, and high frequencies. You will find that sim-ple sealed and vented enclosure designs often yield the most predictable andcontrollable responses. Done properly, these simple enclosure designs canproduce some outstanding in-vehicle results that rival well-built homeaudiophile systems.

UNINVITED NOISES The amount of ambient noise in a vehicle while it is traveling also affects theaudio system. If, for example, there is 90 dB of road noise, the audio systemwould have to play at a level of at least 93 dB for the listener to hear it overthe noise. For most listeners, the difference of 3 dB is the minimum increasein output perceivable by the human ear. Several factors affect the noise floorin a vehicle. Air movement past the vehicle, tire noise, engine and chassisnoise and the resonance of the vehicle interior all affect the amount andnature of the noise floor. The less road noise present in the vehicle, the moreeffective the audio system will be at lower power levels.

Although some cars have more cabin noise than others, any high-poweredcar audio system will attempt to transfer energy into air movement or vibra-tion, whichever is easier. All materials have a tendency to vibrate when sub-ject to specific frequencies or sounds. Most vehicles are made up of thinmetals and light plastics that can easily vibrate or resonate, causing destruc-tive interference either in the form of masking (the vibration overpowers orcolors the audio) or absorption (the vibration is actually stealing energyfrom the sound waves resulting in lower audible output).

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IMPORTANCE OF DAMPING VIBRATIONS AND RESONANT PANELSDamping vehicle surfaces-such as door, floor and rear shelf sheet metal-oftenhelp to keep the noise floor low enough so that it seems that the system hasbecome more powerful. Lowering the noise floor will make the audio systemhave to do less work to achieve a certain sound level. Making the surfacesmore solid in the car also helps to keep road noise to a minimum.Remember, smart system designers figure out how to make an audio systemwaste less power instead of always trying to make more!

One of the best methods of reducing destructive interference due to reso-nance is to damp the panels that surround the speakers. This means increas-ing the mass of the material, and lowering its resonant frequency. This ismost commonly achieved with the application of a damping mat, a self-adhesive rubber or tar-like material that adds more weight to the panel.Damping materials also come as spray-on liquids, roll or brush-on liquidsand non-adhesive foam mats, some of which include a layer of lead foil toincrease the damping properties.

SPEED OF SOUNDThe speed of sound depends on the density of the transmission medium andsomewhat on its temperature. For air at 70° F or 21°C, sound travels at1,130 feet per second (or 344 meters per second). Sound travels much fasterin dense material like wood, metal, acrylic plastics and glass than it doesthrough air.

Transmission Medium Speed (feet per sec.) Speed (meters per sec.)

Air @ 70°F (21°C) 1,130 344

Water (fresh) 4,856 1,480

Wood 10,991 3,350

Steel 16,568 5,050

Aluminum 16,896 5,150

Glass 17,060 5,200

Acrylic (Plexiglas) 5,906 1,800

Speaker Installation Replacement of factory components makes up the majority of today’s mobileaudio system installations. Whether the installation is a source unit orreplacement speakers, the goal is always the same: improve the sound quali-ty of the audio system. Most OEM systems are not designed with soundquality as the primary focus. Automobile manufacturers develop their soundsystems around the existing framework of the vehicle, placing speakerswherever they fit best, not necessarily where they sound best. Placement ofthe sound system rarely takes into consideration the effects of the physicalenvironment or placement and frequency response of the components.Manufacturers generally use the minimum number and size of componentsthey can to limit the production cost of the vehicle.

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As a professional installer, you can do better than just replace the factoryequipment with similar, better sounding products. You can design and installa considerably more entertaining audio system using multiple speakers thatare more efficient and better sounding than any factory replacement speaker.Component speaker systems offer more flexibility and creativity. They allowyou to overcome many of the challenges facing modern car audio systems.Moreover, the choice of placement for the speakers is often just as critical as the choice of speakers themselves. Good speakers in poor locations willalmost never sound as good average speakers in prime locations. The qualityof the speaker plays an enormous role-but only after the position is opti-mized.

Dash LocationsIn older automobiles, the dash was a popular speaker location but that isless so in newer vehicles. Dash locations generally produce good stageheight perception since the sound is “in your face” but are limited withregard to the stereo image. The limitations are due to the considerable differ-ential between the left and right speaker path lengths. In addition, facingspeakers into glass makes the dispersion harder to control or anticipate.

Dash locations offer significant installation concerns because the openings

with significantly shallow mounting depths. Dash locations can also be verydifficult to seal or isolate the rear wave from the front wave since many dashlocations are open around and underneath the speaker. Achieving goodsound quality will require additional time to address these concerns.

Dash locations also present other installation challenges. They are usuallyvery close to the windshield, limiting access for tools and maneuvering ofthe speakers in and out. Stubby screwdrivers and small ratchets with socketattachments are necessary to complete most dash installations. Always beextremely careful with tools so you do not accidentally crack the windshield.

Door LocationsMost new automobiles have factory provisions for speaker locations in thedoors. Even if the factory does not provide for a door location, many timesyou can cut your own hole and install a speaker in the door. This can easilybe accomplished with a reciprocation saw, a metal nibbler, or hole saw anddrill motor. It is critical that you verify the mounting location for clearancebefore cutting. It is also good practice to mark and cut the door panel on the bench first. After cutting the panel, you can relocate it on the door, markthe metal skin of the door to ensure proper alignment and then remove thepanel before cutting the metal.

Door locations are difficult in both stereo imaging and staging because thespeakers’ dispersion is generally directed toward the center of the vehicleand not directly at the listener. The left speaker is also much closer to the listener than the right speaker, which influences side biasing.

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are fairly small, usually accommodating 3 1/2”, 4” or 4” x 6” oval speakers

Door locations generally can accommodate larger speakers (5 1/4” to 61/2”), making them perfect locations for mid-bass or mid-range speakers.

When installing a coaxial or full range type speaker, try modifying thespeaker mount to angle it slightly toward the listener. You also can usespeakers with a swivel-mounted tweeter than can be aimed toward the lis-tener. Component speakers are also a good alternative, since the mid woofercan be mounted in the door and the tweeter can be located higher up on thedoor panel, in the mirror trim cover, or even in the A-pillar (aimed at the lis-teners). Take care not to separate the component tweeter too far from themid-range or the sound will seem as if it is coming from two places ratherthan from one single focused placement.

Other challenges associated with door locations are the moving parts in thedoor, such as windows, locks and door handles. When installing speakers indoors, make sure that they do not interfere with any moving parts. High-endaftermarket speakers can be very deep and may cause clearance issues withthe mechanisms, window tracks and the glass itself. One way to overcomeclearance issues is to build or install a depth reduction spacer.

The spacer can be made of wood or plastic. Remember that wood needs tobe painted to protect it from moisture. When adding spacers, make sure thespeaker remains sealed and verify that there will be enough clearance for thedoor panel to be put back on over the speaker.

To further protect against moisture in door locations, cover the top of thespeaker with something to shield the voice coil and cone material fromwater that may come in from the top of the door around the window sash opening.

Moisture shielding is available in foam or plastic baffles installed into thespeaker opening. Such baffles create a barrier between the inside of the door cavity and the speaker itself. If no speaker baffles are available, youcan make a moisture shield using a simple piece of duct tape over the top of the speaker.

Some door applications may require you to cut the door panel and mountthe speakers on the outside of the door. Always solicit the customer’s permission before modifying the door panel in this application.

REAR DECK LOCATIONSRear decks are very common factory speaker locations. If factory locationsare not provided, many times you can cut your own holes to install speakersin the rear deck. Often the rear deck metal may be pre-cut but the packagetray is not. You can use a rotary tool or razor knife to cut the tray. If themetal is not pre-cut you may need to use a reciprocating saw or hole sawand drill motor to cut a hole. Always cut from the underside up to providethe most room and control of the cutting device. Also pay special attentionto the cutting blade so you do not strike the glass when cutting.

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be painted to protect it from moisture. When adding spacers, make sure thespeaker remains sealed and verify that there will be enough clearance for thedoor panel to be put back on over the speaker.

To further protect against moisture in door locations, cover the top of thespeaker with something to shield the voice coil and cone material fromwater that may come in from the top of the door around the window sash opening.

Moisture shielding is available in foam or plastic baffles installed into thespeaker opening. Such baffles create a barrier between the inside of the door cavity and the speaker itself. If no speaker baffles are available, youcan make a moisture shield using a simple piece of duct tape over the top of the speaker.

Some door applications may require you to cut the door panel and mountthe speakers on the outside of the door. Always solicit the customer’s permission before modifying the door panel in this application.

REAR DECK LOCATIONSRear decks are very common factory speaker locations. If factory locationsare not provided, many times you can cut your own holes to install speakersin the rear deck. Often the rear deck metal may be pre-cut but the packagetray is not. You can use a rotary tool or razor knife to cut the tray. If themetal is not pre-cut you may need to use a reciprocating saw or hole sawand drill motor to cut a hole. Always cut from the underside up to providethe most room and control of the cutting device. Also pay special attentionto the cutting blade so you do not strike the glass when cutting.

Mounting speakers behind the listener can seriously affect the overall soundquality and staging of the speaker system, drawing the sound away from thedash and toward the center or rear of the vehicle. Speakers mounted in therear deck should be attenuated to provide ambient fill rather than dominatesound.

There is usually an abundance of space on the rear decks to fit any sizespeaker, although there may be depth issues with the trunk supports insome vehicles. Rear deck speakers may also offer the same restrictions asthose mounted in the dash, due to the close proximity of the back glass tothe rear deck. Always be cautious when installing rear deck speakers so asnot to damage the glass.

KICK PANEL LOCATIONSVery few manufacturers use kick panels as factory speaker locations, butkick panels are one of the better locations. They allow for the speakers to beaimed at the listener and generally offer the most similar distances betweenthe speaker and the listener, providing good stereo imaging and staging.Since few automobiles have factory kick panel locations, you will most likely

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Figure 140. Custom CenterChannel Speaker Installation

Attempt to install a center

speaker in a location that does

not face directly into the front

windshield. The glass affects

the sound dispersion of the

center channel, many times

in a negative fashion.

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The Direction of SoundHumans use both ears to locate a sound’s direction. Assuming a head diameter of 6 inches (or 0.5 feet), humans can determine the direction cuefrequency as 2,260 Hz. Above 2,260 Hz, they will identify a sound’s directionprimarily by amplitude differences at each ear. Since there is negligible diffraction, sound arriving at one ear will not bend around to the other ear.Between 700 and 2,260 Hz there is a transition zone, where direction is deter-mined by both amplitude and time-of-arrival differences at both ears. Below700 Hz, internal time-of-arrival analysis no longer works because diffractionbecomes more prominent and our ears cannot tell where the sound is comingfrom. At bass frequencies, sound becomes completely non-directional.

Stereo ImagingThe primary concern with stereo imaging is equalizing the path length (distance from the speaker to the ear) of the sound waves coming from thespeakers. Proper stereo imaging occurs when left and right speakers, withthe same phase and polarity, are equidistantly placed and aimed at a centerlistening position. If the left and right channel information reaches the earsat the same time, the imaging should be fairly accurate.

Ideally in the mobile environment, reproduced music should be perceived to extend outside dashboard boundaries, above, below and side-to-side for athree-dimensional effect. You should be able to locate individual instrumentsrelative to each other in the stereo track. This is especially important inhigh-end mobile installations, since component systems are often specified,with tweeter/mid-range placement and correct wiring polarities being criticalconcerns. To favor a driver’s listening position, stereo imaging can be adjust-ed with a left/right fader or through an external DSP component that storessettings for different passenger positions (although there is no real substitutefor absolutely equidistant path lengths).

6” frequency = speed of sound/one wavelength at head diameter frequency = 1130 / 0.5 = 2,260 Hz

Above 2,260 Hz, sound direction is detected by amplitude to closest ear.

Between 700 and 2,260 Hz, sound direction is detected by amplitude andtime-of-arrival differences at both ears.

Below 700 Hz, sound direction is harder to detect, since diffraction ofbass frequencies around head causes similar amplitudes at both ears.

Equidistant left and right speaker placement is difficult to achieve physically.The mid range of the frequency band is easiest to notice when the soundappears biased to one side. Side biasing is a common problem when usingsome factory speaker locations.

Electronic DSP or time delay can compensate for an offset in physical alignment by delaying the sound coming from the closest speaker by a fewfractions of a second (measured in milliseconds). Generally a delay of

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1 millisecond will be required for each 12” of offset between the left andright speakers. Remember though, whatever time delay is implemented to better suit one listening position will have an inverse effect for other listening positions. This is why the widespread use of time correctionprocessors in the vehicle is not common.

StagingThe mobile environment offers a unique sound perception effect known asstaging. Staging defines the speaker system’s accuracy in conveying audibleinformation about the height and depth of the sound stage, placing theartists and instruments correctly across the vertical sound field in front ofthe listener. In addition to a left/right balance control, a number of premiumsource units also provide a front/rear fader to help create the staging effect.

The primary concern with staging is placing the front speakers on axis with the listener so that the sound is directed at the listener in a moreupward or head-on dispersion. This may be difficult to achieve physicallybut should be taken into consideration, tilting speakers toward the listenerwhenever possible.

Ideally, ambient sounds like reverberation effects (via an external DSP)enhance the sound coming from the front speakers without drawing yourattention to the location of the rear speakers. The rear speakers may bemuch more pleasant to listen to when the output levels are 3-6dB lower than the front speakers. This represents a difference of 25-50 percent of thepower level driving the front speakers if the same speaker sensitivity appliesto both pairs of speakers.

The recording industry is promoting discrete, multi-channel encoded CDs,DVD-Audio and SACD as viable music playback formats for the car. Theassumption is that some music discs could have a “home” and “car” mix tobetter suit each listening space, but it remains to be seen what effect this will have on the mobile environment.

Absolute PhaseThe term “absolute phase” represents the physical relationship of soundwaves to each other using a known reference, and is measured in degreesfrom 0 to 360. This term also considers all sound sources in the listeningspace. The simple version of speaker phase relationship is more clearlyunderstood as polarity in a single speaker.

If a speaker pushes the air (compression) first and then pulls the air(rarefaction) second, this is considered “positive phase” or “in polarity.”This is positive-to-positive and negative-to-negative, electrically speaking.

If a speaker pulls the air first and then pushes the air second, this isconsidered “negative phase” or “out of polarity.” This is positive-to-negative and negative-to-positive, electrically speaking.

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When two speakers are mounted next to each other and push and pull at thesame time, this is considered absolute phase. Both speakers are doing thesame thing and are working complementary to one another. The soundwaves work together as exact copies, adding acoustic output (or SPL). This is also known as constructive interference.

If the speakers are not playing the same thing at the same time, the speakersare often assumed to be out of phase by 180°. In this case, the sound wavesare acting against each other-exact opposites canceling each other out. Thisis known as destructive interference. Unfortunately the true pursuit ofabsolute phase is not always that simple.

Phase problems can exist anywhere between 0 and 360 degrees as a result of the physical relationship between speakers in a system. If a mid-rangespeaker mounted in a door is directed toward the center of the vehicle andthe tweeter is mounted in the A-pillar directed toward the listener, the distance and difference in mounting orientation can put the sound wavescoming from each speaker out of phase from one another. This may causeundefined mid-range and high frequencies that do not sound natural.

Absolute phase problems are most common and noticeable in the sub-bassfrequencies as a result of the placement of the subwoofer in contrast to theother speakers. It is possible the sound from the mid and high speakers will reach your ear in a forward pressure wave (positive phase) and-due todistance the sound from the subwoofer must travel from its location-mayarrive as a vacuum wave (negative phase) when it reaches your ears. Thatresults in a delayed, sluggish sounding bass called a node of low pressure.The node of low pressure comes about because of the physical differences in distance between the speakers, not because you hooked up positive andnegative terminals incorrectly. This happens in many vehicles.

The easiest way to identify absolute phase issues is to listen to the system.These guidelines demonstrate some methods to compare results whenchanging the polarity of an audio signal:

If the mid-range and high frequency speakers sound blurry or unde-fined, try reversing the polarity-one speaker at a time-and listen again. If no noticeable change takes place or the sound becomes more unde-fined, reverse the polarity back into the original position on the selectedspeaker and move on to a different speaker. Remember it is easier toidentify phase anomalies in mid-range speakers than in high frequencytweeters.

If the bass sounds sluggish or delayed, try reversing the positive andnegative wires going to the subwoofer(s) and listen to the system again.If the sound is cleaner and more accurate, leave it wired this way. Youmay be able to complete this test without physically rewiring the speak-er, since many amplifiers or sub woofer pre-outs on a headunit have a180° phase switch that can accomplish the same polarity reversal.

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It is important to understand that switching phase exactly 180° is nothingmore than inverting the polarity of the audio signal going into the audiocomponent or speaker. The physical distance of each speaker to the listenerwill have an inherent absolute phase difference from other speakers in thesystem. Your goal is always to have all speakers creating the same move-ments (pressure or vacuum) at the same times. This results in absolutephase, yields the best use of amplifier power, and creates the opportunity forthe best sound with the least amount of unnecessary equalization.

Effects of Differences in Multiple Path LengthsThe precedence effect-or Haas effect, named after German researcher HelmutHaas-describes the ability of our ears to lock onto the first arriving soundeven though other, louder sounds may follow. As long as the delayed soundsarrive no later than 25 milliseconds afterward and are no greater than 10 dB,the human brain will fuse them together as a single reinforced sound. Othersounds that do not meet these two conditions and are not masked will beheard as distinct echoes. In mobile installations, speakers cannot be mount-ed far enough away to produce distinct echoes at the listening position.However, in lower end systems, you may hear a left- or right-side bias(caused by amplitude reduction) based on the increased distance of onespeaker from the listening position.

More subtle effects are cloudy placement of images that move from left-to-right and front-to-back as the frequency from the recorded instrumentchanges. For a pair of tweeters, the wavelengths are really too short to causeserious anomalies in frequency response (as measured by a one-third octaveRTA), but the sound may peak in one listening position and yet sound dif-ferent for a slightly adjusted head position because of comb filtering. Thiscan cause narrow-band “suckouts” at frequencies when wavelengths corre-spond to the difference in distance from the two sources to the listener.

Sound QualityThe quality of the received sound depends on a number of system perform-ance measurements, including distortion, noise and separation, as well asfactors such as direction, imaging and staging. You can optimize the latterwith proper placement of speakers and enclosures in the vehicle. It is impos-sible to overstate the importance of proper installation techniques, such aswiring, enclosure construction and acoustic treatments.

INSTALLATION OF FACTORY REPLACEMENT SPEAKERS Identify the polarity of the wires using the factory speaker and a 1.5vbattery or, preferably, a phase checker. You may also look up the properwire colors on a vehicle-wiring diagram, though you should always verify polarity.

Connect the speaker wire to the speaker.

Secure the speaker in the factory location.

Aim coaxially mounted tweeter (if applicable).

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Always make sure that a

replacement door speaker is

equally well coupled to the

opening in the panel through

which the sound will travel.

Poor coupling results in

unnecessary cancellations.

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Make sure that the speaker is completely baffled (sealed front from rear).

Observe and maintain adequate speaker-to-panel opening couplingfor maximum performance.

NON-FACTORY LOCATIONS Double-check that the speaker will indeed fit in the proposed location.

Make sure that the speaker will not interrupt operation of factorymechanisms such as window cranks, motors, windows and controlarms.

Using a template or a hole saw, mark the opening on the panel.

Make sure both left and right speakers are mirror imaged (located in exactly the same place on both sides of the vehicle).

Use a razor knife to cut cloth, vinyl or carpet type materials beforecutting the hole in the panel.

Note: Always demonstrate caution and care when cutting and use the appropriate safety devices such as eye and ear protection. No matterwhat cutting method you use, be sure to support the panel so that vibrationdoes not damage it. Be sure that the window is completely rolled up before cutting in a door.

Cut the panel using an air saw, razor knife or hole saw.

If using a hole saw, pre-drill the pilot hole before sawing.

Replace the panel on the door or body part and transfer the hole onto the metal.

Remove the panel and inspect the area to ensure clean cutting; lookfor wire harnesses, etc.

Cut the metal using an air saw, metal nibbler, hole saw, etc.

When adding speakers in a non-factory location you generally willneed to run speaker wire to that location.

Neatly secure all wiring to factory harnesses with wire ties, or affixduct tape to the floor every 12”-18” under the carpet and behind factorypanels.

When running wire into a door, always use the factory wire bootwhere applicable.

If it is not possible to run the additional wire through the factory bootor if a factory boot does not exist, you will need to create your own boot.

Always locate the entry hole into the door at lower than the entryhole into the side of the vehicle. That will prevent water from followingthe boot into the kick panel, where it may damage sensitive vehicle elec-tronics.

Always install a grommet in both holes.

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Always protect the wire with a clear nylon tube or split loom tubing.

Never drill the access hole on the vehicle side in the face of the door jam.

Always drill your access hole through the side of the door jam orkick panel area to prevent damaging the wire when the door is closed.

Connect the speaker wires. Maintain proper polarity!

Secure the speaker in the opening.

Try to ensure all screws are secured into metal or use “speed” clips ifnot securing into metal.

Make sure that the speaker is completely baffled (sealed front fromrear).

Install the grills and make sure that they are straight and symmetrical.

Install and set up the provided crossover network with a componentset.

Adjust tweeter level and phase.

Adjust axis mount settings as required.

Make your connections to the radio or amplifier as necessary. Observeproper polarity.

Reassemble the vehicle.

Verify proper cosmetics, fit and finish before delivering the vehicle to the customer

TIPS FOR COMPONENT SPEAKER PLACEMENTWhen installing a component speaker there are some common installationconcerns.

1. Locate the tweeter as close to the woofer as possible, not to exceed adistance that is more than the diameter of the mid-range woofer. For example: If you are installing a 61/2” component set, the tweetershould be no more than 61/2” away from the mid-woofer. This will helpprevent phasing issues.

2. Mount the tweeter on the same vertical plane as the woofer. This willhelp avoid time alignment issues.

3. Mount the tweeter below the mid-woofer when applicable, such as in a kick panel application. This addresses a time alignment concernknown as the zero-delay plane. If the tweeter is mounted below thewoofer the combined psycho-acoustic effect will actually lift the soundstage.

INSTALLATION OF FULL RANGE SPEAKERS AND MID-WOOFERS

It is important to make sure the speaker has a good seal around itsmounting location. Do not allow any air to leak by the speaker becausethe speaker gasket is defective, or the mounting surface is larger thanthe speaker.

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If the sound waves from the back of the woofer reach the soundwaves from the front of the woofer, you will get cancellation of the lowfrequencies. If you encounter small gaps around the woofer you can useduct tape to seal the gaps. If there are large gaps all the way around thewoofer, cut a baffle board out of wood or plastic that will cover all thegaps. If the baffle board is wood, make sure to paint it to protect itagainst moisture.

INSTALLATION OF TWEETERS

Flush Mount - Flush mounted tweeters are one of the more visuallypleasing mounting applications. Flush mounting will require you to ver-ify clearance before any cutting. Depending upon the panel material tobe cut, use the template provided by the manufacturer in conjunctionwith a razor knife, reciprocating saw or a hole saw of the correct diame-ter. Flush mount tweeters will generally have a mounting cup or assem-bly into which the tweeter itself is mounted. After cutting the hole, besure to securely mount this cup or assembly into the panel beforeinstalling the tweeter. Use common sense if using sharp tools aroundupholstered surfaces and protect the upholstery accordingly.

Surface Mount - Surface-mount tweeters are not as visually pleasingas a flush mount because the tweeter will protrude from the surface.Surface-mount tweeters will generally have a mounting cup or assemblyinto which the tweeter itself is mounted. This mount will need to bescrewed or bolted from the back side of the panel. If mounting to a plas-tic surface, use a nut, bolt and washers, or “speed” clips to prevent thetweeter mount from falling off the panel over time.

Axis Mount - An axis mount is one of the easiest tweeter mountingapplications since the tweeter is mounted on top of the woofer. Followthe manufacturer’s guidelines when installing an axis mount tweeter.Most component systems that offer an axis mount application shouldhave some type of switch or jumper inside the crossover to configurethe frequency response of the speaker systems. This compensates for thechange in frequency response of the woofer once the tweeter is suspend-ed over it.

Crossover - The crossover should be mounted where it can be easilyaccessed. Some internal adjustments on the crossover need to be acces-sible when tuning the system. Some good locations for mounting thecrossover are in the kick panel, under the seats and under the dash. Youcan also mount them in the door panels if you install them between thevapor barrier and the door panel. Never mount the crossover by anypower wires. If the crossover is mounted near power wires, you will getinduced noise through the speakers.

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Remember to keep

passive crossovers away from

sources of radiated noise.

Additionally, install them in a

location for ease of tweeter

level adjustment (when so

equipped).


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Digital and Multi-Channel Sound AUDIO ENCODING FORMATS

Pulse Code ModulationPCM (pulse code modulation) is a digital scheme for transmitting analogdata. The signals in PCM are binary. As you learned in Chapter 1, binarynumbers are represented by only two digital possibilities, either a 1 (high) ora 0 (low). Digital audio is just ones and zeros no matter how complex theanalog waveform is. Using PCM, it is possible to digitize all forms of analogdata, including full-motion video, voices and music.

To obtain PCM from an analog waveform at the source of the audio path (likea microphone or multi-track recording console), the analog signal amplitudeis sampled at regular time intervals and converted into a digital representa-tion. This is the analog to digital (or A/D) conversion. The sampling frequen-cy-the number samples per second-is several times the maximum frequencyof the analog audio waveform. The theory known as the Nyquist Limit statesthat the sampling frequency of the audio signal must be twice the upper limitof the highest audio signal, so that the sampling is indistinguishable to thehuman ear. This is why PCM audio is sampled at 44.1kHz (exactly twice22.05 kHz, which is well beyond the capability of human hearing).

The instantaneous amplitude of the analog signal at each sampling is round-ed off to the nearest of several specific levels. This process is called quantiza-tion. The number of binary levels is always a power of 2. The digital outputof a pulse code modulator is now a series of binary numbers, each represent-ed by some power of 2 bits. The compact disc format uses 16 bits of data.DVD-Audio uses 24 bits of PCM data. The theory is that having a greateramount of bits (audio data) increases the overall sonic realism of the record-ing, both in audio content and signal-to-noise ratio.

At the destination of the audio software signal path (such as a CD player), apulse code demodulator converts the binary numbers back into pulses hav-ing the same quantum levels as those in the modulator. These pulses areprocessed to restore the original analog waveform. This is the digital to ana-log (or D/A) conversion process. A signal does not have to be a PCM signalto move between the analog and digital domains. PCM is a linear format,which means there is no additional encoding for distribution of the digitalinformation into any other form than it was originally sampled.

In addition to PCM, another form of converting analog signals into digitalsignals exists. This is known as delta-sigma or “one-bit” A/D and D/A con-version. Delta-sigma is employed in some D/A converters of early mobile CDplayers. The technique is now the basis for the SACD (super audio compactdisc) data format. The type of delta-sigma A/D conversion used in makingSACDs is called direct stream digital (DSD). The advantage of this techniqueis the amount of data that can be throughput in a particular amount of sam-pling time. Read more about SACD and delta-sigma conversion in the subse-quent SACD sections.

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Compressed Digital Audio (Perceptual Coding)In 16-bit PCM encoding systems, the goal is to digitally reproduce the wave-form of an audio signal as accurately as possible, given the storage space.The fact is, though PCM encoding is a great way to transfer high quality dig-ital audio, it is rather bulky when lots of music needs to fit into a somewhatsmall space. This is why various forms of digital audio compression havebecome popular. Compression allows more music to fit into a smaller space,but at what cost to the quality of the sound?

MP3 (MPEG 1, Layer 3) audio compression is arguably the best-knowncompression format in use today. MP3 uses some inevitable truths abouthuman hearing to figure out how to compress the audio with the best audi-ble results. Since human hearing has all sorts of factors that are not linear,some areas of audio reproduction can be manipulated to achieve a good-butnot perfect- result. Audio compression formats use a technique known asperceptual coding, which encodes an audio signal so the human ear will per-ceive it as close to the original without actually consuming the same spaceas a PCM digital audio conversion. You might say that PCM attempts to cap-ture an audio waveform as it “actually is” while perceptual coding (as inMP3) attempts to capture an audio waveform as it sounds to the human ear.Though some humans have more refined ears than others do, it is safe to saythat you can achieve some balance between audio quality and storage space.

Perceptual coding is done by making a reference to a psychoacoustic model,essentially a mathematical representation of the way in which humans bothhear and perceive changes in sound. When psychoacoustics are in place, itbecomes interesting to see what humans hear versus what we think we hear.The process of thinking as we are hearing means that humans prioritizesome sounds while we ignore others. This is called masking. By using mask-ing techniques that are similar to human hearing, audio compression tech-niques such as MP3 allow some of the audio that the human ear does notrecognize anyway to be discarded. Audio that is not recognized is consideredirrelevant in the compression process. Irrelevant audio information is there-fore not necessary to store and that is how MP3 makes file sizes smaller.

Masking occurs because human hearing is adaptive and adjusts to suit thedominant levels of sound and noise in a given environment, such as an auto-mobile. Here is an example: a sudden handclap in a quiet room may seemloud, but if that same handclap had been preceded by a gunshot, it wouldnot seem nearly as loud. Here is another example: while in a quiet recordingstudio, the sound of an electric guitar might seem to dominate the mix, upuntil the moment the drummer hits a particular cymbal, at which point theguitar seems to briefly drown out because the cymbal is the “new sound” theear identifies. Both of these are examples of masking in the time domain andthe frequency domain. When two sounds occur simultaneously (or near-simultaneously), one is partially masked by the other. This phenomenondepends on the relative volume and frequency content of the sounds.

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The Haas effect describes the relationship of time domain variations betweentwo sounds. It states that as long as the delayed sounds arrive no later than25 milliseconds from the primary sound (and are no different than 10 dBsound pressure level), the human brain will fuse them together as a singlereinforced sound. This is one element of masking that enables perceptualcoding to get away with removing much of the irrelevant data that conven-tional audio signal coding stores. This does not mean that all audio datadeemed irrelevant in perceptual coding is completely discarded; it is simplyassigned fewer bits of data than the audio data deemed “relevant.” This hasthe effect of introducing some distortion, but the distortion is typically con-fined to the masked elements and is barely audible. The audibility of the distortion is simply a function of the audio content (voices are easier to compress than full musical performances) and the resolution of the listener’s ears.

Using fewer bits of data to represent the masked elements in a recordingmeans that fewer bits overall are required. This is how MP3 coding succeedsin reducing audio files to be less than 1/10th of their original PCM size, withlittle or no noticeable degradation in sound quality (depending on your earsand the system on which the MP3 audio is played back). MP3 encoding sup-ports native sampling frequencies of 32 kHz, 44.1kHz and 48 kHz. The bitrate of the encoding is chosen at the time of encoding and can be as much as320kbps to as little as 16kbps. Higher bit rates are recommended for musicand lower bit rates are suitable for the spoken word or background music(such as music on hold for a telephone system). The very best listeners maystill notice differences between a native CD format and a compressed MP3format, even at high bit rates.

Dolby advanced audio coding (AAC) is a new perceptual coding techniquewith similar bit rate capabilities as MP3, but claiming to have file sizes up to30 percent less in high resolution (128 kbps) formats. AAC is part of theMPEG 2 and MPEG 4 digital media standards. (Remember MP3 reflectsMPEG 1, Layer 3). Given the software size, encoding application and play-back device, AAC provides sample rates of up to 96 kHz and broadcast qual-ity audio at 320 kbps for a 5.1-channel encoded material.

Microsoft’s Windows Media Audio (WMA) is much like MP3. The WindowsMedia compression codec is similar to MP3 but produces smaller files. WMAperforms very well at lower bit-rates and is reported to produce qualityindistinguishable from the original CD at 128 kbps, which then compressesto around 48 kbps (about a third of the size of MP3). WMA is designed tocope with a variety of sounds, from low bandwidth speech to CD-qualitymusic. Recent developments in audio compression and decompression technology enable WMA to be much faster and to take up less file spacethan older compression formats. While not all in-dash MP3 capable head-units will play WMA files, many hard drive-based mobile audio storagedevices will store and play back many file formats including MP3, WMA, WAV and others.

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Wave files (.WAV) are a standard audio file format that traditionally usesPCM for full audio resolution. WAV files are typically four to five times thesize of an MP3 or other compressed 2-channel audio file format. A typical700MB CD supports about 80 minutes of PCM audio in a .WAV file format.Recently the WAV file format has been adapted to store its audio data inother compressed formats.

Lossless Compression TechniquesUncompressed PCM linear conversions are somewhat limited on storagespace if more than two channels are required. The 16-bit audio CD as weknow it is simply a 2-channel source format. Lossless compression allows agreater number of channels to be put into the same space as two channelsnormally occupy, without compromising the overall audio reproductionquality. One current 2-channel format known as FLAC (free lossless audiocodec) is available for use in several popular encoding software packages.FLAC files will play on any FLAC-enabled mobile audio playback device,though the file sizes are considerably larger than a WMA or MP3 file. Still, a FLAC file is about half the size of a .WAV file with few negativeaudible effects. Lossless compression is especially useful in the new DVD-A and SACD formats. Here is an analogy to describe lossless compression:

“If you had a load of bricks to transport to a building site, you could justthrow them in the back of a truck and carry them, or at least some of them,to where they were needed. However, if you took the time to stack themneatly, you would get more bricks in the same truck and could transportthem more efficiently- perhaps all in one trip!”

That is the principal advantage of lossless compression. You transport thebricks in the most efficient manner by packing them closely together. Andyou still have all the bricks at the end of the ride. Read more about DVD-Audio and SACD in the “Discrete Multi-Channel Encoding (LosslessCompression)” section.

Matrix Audio Encoding (Dolby Surround) Dolby Surround is an analog-based matrix encoding process that essentiallypacks four individual channels (left, center, right and surround channels)onto 2-channel stereo soundtracks. Each of the four channels has been specially encoded onto the 2-channel stereo soundtracks of Dolby Surroundprogram material such as VHS movies and TV shows. A Pro Logic decoderunpacks the four channels upon playback.

Dolby Pro Logic is a matrix-decoding process that decodes four channels of surround sound. If there is no Pro Logic decoder, the matrix-encoded program material simply plays in normal 2-channel stereo. Matrix encodingis an analog process that simply mixes a left and right audio signal togetherand may limit the bandwidth upon decoding for certain applications.Depending on the applications (front channels or rear channels), the matrix can be decoded as “L+R” (left plus right) or “L-R” (left minus right).

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Lossless compression

schemes aim to recreate the

original audio material with

few (if any) negative audible

effects.


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Front center channels or mono subwoofers are typically L+R while rearspeakers are typically L-R and bandwidth-limited.

Discrete Multi-Channel Audio Encoding (Lossy Compression)Taking the idea of perceptual coding a step further, many multi-channel for-mats offer discrete channels above and beyond the 2-channel world. This isall made possible (as well as practical) by technologies of digital audio andperceptual coding. Two of the most recognized multi-channel formats arefrom Dolby Labs and Digital Theater Systems (DTS).

Dolby Digital 5.1 and DTS 5.1 are methods of transmitting and storing 5.1-channel soundtracks via newer digital media such as DVD, digital cable, dig-ital broadcast TV (DTV) and satellite transmissions. Unlike the DolbySurround encode/Pro Logic decode process, which sacrifices channel separa-tion to get surround onto any stereo soundtrack, Dolby Digital 5.1 and DTS5.1 are discrete digital encoding systems that keep the multiple channelsfully separated throughout the encoding and decoding process. In additionto having full-range front left, front center, front right, left surround andright surround channels, Dolby Digital 5.1 and DTS 5.1 soundtracks carry asixth (.”1”) channel recorded with low-frequency effects (those bass rumblesand booms you feel as well as hear in a well-equipped cinema). The sixthchannel is called the LFE channel for low frequency effects.

Discrete Multi-Channel Audio Encoding (Lossless Compression)DVD-Audio and SACD software formats also use discrete channel encodingand proprietary decoding methods to carry six separate channels of digitalaudio. The main difference between DVD-A and SACD and other formats isthat the encoded multi-channel audio signal is generally a music selectionrather than a surround sound movie soundtrack. In addition, the inherentlosses of perceptual coding techniques are virtually eliminated in what bothDVD-A and SACD call lossless compression.

DVD-A uses a lossless compression format called Meridian Lossless Packing(MLP) to reproduce its superior audio playback with a frequency response of5-50 KHz. DVD-Audio requires a DVD-A player for true playback of theMLP audio tracks. Some special discs are available that have Dolby Digital orDTS-encoded audio material in the video zone of the disc. A normal DVD-Video player can access the video zone. Read more about DVD-Audio in the“Multi-Channel Audio Formats” section.

Like DVD-Audio, SACD offers 5.1-channel surround sound in addition to 2-channel stereo mix on a single disc. SACD uses Direct Stream Digital (DSD)recording, a proprietary Sony technology that converts an analog waveformto a 1-bit signal for direct recording, instead of the PCM and filtering usedby standard CDs. DSD uses a lossless compression scheme (different thanMLP) and a sampling rate of 2.8MHz to improve the complexity and realismof sound. Read more about SACD in the “Multi-Channel Audio Formats”section.

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When connecting a DVD-

Video player into a Dolby

Digital or DTS decoder via

POF cable, all six channels are

digitally contained within that

single connection. The

decoder must unpack and

decode each channel to

provide the discrete 5.1

channels of output.

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To read more about each of the unique methods of each format for encodingand decoding, please read the additional topics in this chapter regarding“Audio Source Formats,” “Video Source Formats” and “Multi-ChannelDecoders.”

Fully Discrete and Discrete plus Matrix (Hybrid Formats)With respect to soundtracks, such as those on movies and DVDs, 5.1 meansthat the soundtracks are recorded with five main channels: left, center, right,left surround and right surround, plus a low-frequency effects (LFE) basschannel. Some movie soundtracks use a variation on 5.1, either DolbyDigital Surround EX or DTS Extended Surround (ES).

With the Dolby Digital Surround EX format, a third surround channel ismatrix-encoded onto the left and right surround channels of 5.1 sound-tracks, and may be decoded at the cinema’s or home listener’s option due tothe channels’ inherent compatibility. Because the left and right surroundchannels carry the extra surround information as “matrixed” information,Dolby Digital Surround EX encoded soundtracks are still regarded as 5.1soundtracks. As of this writing, Lucasfilm/THX hold the rights to marketthis technology for home use.

DTS-Extended Surround (ES) also adds a center-surround channel to theexisting 5.1-channel array, but is fully discrete. DTS-ES is the only formatthat can deliver all 6.1 channels as discrete. DTS-ES is fully compatible withall types of multi-channel playback systems. All sounds will be heard,whether played back as discrete 6.1, matrix 6.1 or on a 5.1 system. In 5.1systems, the encoded rear center channels are spread to the left and rightsurround channels. Currently, no mobile A/V processors offer DTS-ESdecoding for the automobile.

With respect to playback in a home theater, the terms 5.1, 6.1 and 7.1 meanthat there are five, six or seven main speakers, plus a subwoofer, in the play-back system. The subwoofer reproduces the LFE channel recorded on 5.1soundtracks, plus any bass the main speakers cannot handle. The differenceis in the number of surround speakers: two in a 5.1 system, three in a 6.1system and four in a 7.1 system.

Obviously, a 5.1-channel soundtrack can be played on a 5.1-speaker system.But it can also be played on a 6.1- or a 7.1-speaker system. To do this, thetwo surround signals on the 5.1 soundtrack are spread across the three orfour surround speakers. This distribution can be accomplished by a DolbyDigital EX decoder, DTS-ES decoder, a THX quality Surround EX decoder orother proprietary methods in home theater equipment.

The number describing the soundtrack (i.e., 5.1) does not have to match thenumber applied to the speaker system. It is even possible to play 2-channelstereo content over these multi-speaker systems by using a matrix surrounddecoder such as Dolby Pro Logic 2 or Lexicon L7. The delivery format and

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the speaker configuration are independent, and it is the decoder’s job tobridge them effectively. Dolby Pro Logic 2 processors are available from sev-eral aftermarket mobile electronics companies as well as being built intomany of the hideaway sub chassis of many flip-up screen headunits. If amobile audio component contains Dolby Pro Logic 2 matrix processing, itwill certainly indicate that.

OEM mobile audio systems already feature matrix decoding that allows thesurround effect with normal 2-channel audio formats such as CDs or cas-sette tapes. Many Volvo vehicles feature Dolby Pro-Logic or Dolby Pro-Logic2 and the 2002-2004 BMW 7 series features a premium option of theLexicon L7 audio system.

MULTI-CHANNEL AUDIO SOFTWARE FORMATS

DVD-AudioDVD-Audio is a new 24-bit format that delivers high-fidelity audio contenton the DVD media format. It offers stereo and surround sound capability, as well as a maximum of two hours of 2-channel audio per layer at24bit/192kHz sampling or 1.5 hours of 5.1 surround audio per layer at24bit/96kHz sampling. As with the DVD-Video format, two layers per sideare possible, although DVD-Audio will commercially begin as single side,single layer when it appears in stores, at least for the immediate future. Once the market penetration increases (as DVD-Video has), the potentialexists for a wider variety of configurations.

The 24-bit DVD-Audio format has a maximum of 8 channels per layer (a5.1-audio track with an additional 2-channel audio track). A 24-bit DVD-Audio track uses MLP, a lossless compression format, to get more data intothe allotted space while still being linear on the other end. DVD-Audio willsupport 16-, 20- or 24-bit formats and sampling rates of 32, 44.1, 88.2, 96 and 192kHz to maintain flexibility with existing formats of audio data.

SACDThe Super Audio Compact Disc (SACD) format is another multi-channelaudio software format that is heavily backed by Sony and Philips (whoinvented the conventional CD). Although the format differs from DVD-Awith respect to A/D conversions and sampling rates, both are consideredlossless compression carriers for multiple discrete channels of audio. SACDoffers only a single-sided format, but also has the potential of a second layerand a “red book” within the second layer, which is a data layer that will play back on a conventional 16-bit CD player.

The future of mobile audio will contain many avenues for getting multiplechannels of sound into the vehicle. Via discretely encoded software ormatrix processing, the future of car audio is more entertaining because the“experience” of listening to surround sound can be taken on the road.

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STAND ALONE DECODERSDolby Pro Logic is a matrix decoder that decodes the four channels of sur-round sound that have been encoded onto the stereo soundtracks of DolbySurround material such as VHS movies and TV shows. Dolby Surround is amatrix-encoding process that in essence folds left, center, right and surroundchannels onto stereo soundtracks. A Pro Logic decoder then unfolds the fourchannels on playback. When a Pro Logic decoder is not present, the encod-ed program simply plays in regular 2-channel stereo.

Dolby Pro Logic 2 is a more robust matrix-decoding technique that derivesfive full range channels from a 2-channel source, even it has not been specif-ically Dolby Surround-encoded. It is an improvement over Dolby Pro Logicbecause the rear channel decoding is done in stereo, rather than mono, andthe channels are full range (20Hz to 20kHz) whereas the rear channels arebandwidth-limited in the older Dolby Pro Logic format. When processingencoded material such as movie soundtracks, the sound is somewhat likeDolby Digital 5-without the “point 1.” When processing standard 2-channelstereo material (such as 16-bit audio CDs), the effects present a wider, morespacious field of sound. These advancements make Dolby Pro Logic 2 espe-cially well suited to deliver surround sound in the car with current 2-chan-nel audio source formats as well as with DVD-Video movies. Rememberthough, that the Dolby Pro Logic 2 matrix processing does not provide bassmanagement (the subwoofer crossover and level control) unless it is con-tained elsewhere in a built-in (integrated) preamp processor.

The potential advantage of the Dolby Pro Logic 2 processor hardware in thecar is that it takes standard 2-channel RCA audio inputs. With RCA inputson board, a digital input is not required to process a Dolby Pro Logic 2effect, whereas a Dolby Digital 5.1 or DTS 5.1 format would require a digitalprocessor with a digital input to function in a mobile A/V surround system.

Dolby Pro Logic 2 is well suited for any source delivered in-or originatingin-a 2-channel format. This means MP3 and WMA compressed audio, FM or satellite radio (but not AM), cassettes, CDs, DVD-V discs outputting 2-channel PCM data through a D/A converter, and many other commonaudio formats can all benefit from multiple channels where originally onlytwo channels were input. Dolby Pro Logic 2 processors are available fromseveral aftermarket mobile electronics companies. Again, the bass manage-ment function may be part of a feature set within the particular unit (not normally part of the Pro Logic 2 processing matrix), especially if Pro Logic 2 is controlled exclusively from the headunit.

DTS Neo:6 is an advanced matrix decoder. It will take any 2-channel sourceand expand it into five or six channels, depending on the speaker layout ofthe audio system. Two-channel sources include VHS tapes, broadcast televi-sion, 16-bit 2-channel stereo CDs, and 24-bit DVD-Video discs. DTS Neo:6provides separate, optimized modes for stereo music source material andmatrix surround motion picture soundtracks. DTS Neo:6 also decodes a

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Margin Notes

Dolby Pro Logic 2 takes

two channels of stereo audio

input and provides five

channels of output. It does

not have a .”1” or LFE channel

all by itself, although an

integrated component may

offer supplemental subwoofer

outputs with a LP crossover

and level control.


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center-surround channel from extended surround matrix soundtracks suchas Dolby Surround EX. Currently there are no signal processors for mobileaudio applications featuring DTS Neo:6 decoding capabilities.

It is important to note that any standalone decoder, regardless of format,depends on a dedicated center speaker to fully reproduce the intent of thedecoding process. Without center channel speakers, the entertainment expe-rience of a multi-channel mobile audio system is going to be only moderatelymore entertaining.

Vehicle Disassembly for Mobile Video System Installations When a video system installation is taking place, many different levels ofintegration and disassembly may be necessary. The key to understanding thedisassembly task is to establish which type of video installation is to beinstalled. There are two distinct categories of mobile video installations:

Integrated Mobile Audio/Video Systems - In some applications, a full-blown mobile theater experience is the intent. In an integrated mobileA/V system, both the video and audio portions are a part of the mainaudio system. Typically the in-dash headunit controls them, allowingthe audio portion of the video experience to play through the amplifiersand speakers in the audio system. If a system contains processing suchas Dolby Pro-Logic 2, Dolby Digital or DTS, the system installation alsowill likely involve the same scale of disassembly as a large audio systeminstallation. Rarely, if ever, is the fully integrated mobile A/V installationa quick one-day installation.

Rear Seat Entertainment Systems - These systems are almost entirelyseparate and standalone from the existing main audio system, whetherOEM or aftermarket. The rear seat entertainment system essentiallyallows a visual entertainment source for rear seat passengers and typical-ly involves an alternative listening method such as wired or wirelessheadphones. Many rear seat entertainment solutions offer a simple self-contained monitor and source unit with headphone transmitter circuitrybuilt in to facilitate quick installation. Some rear seat entertainmentinstallations may connect into the main audio system with simple methods such as an FM modulator or AUX input. Most rear seat entertainment installations are completed the same day.

Here are the parts that are common for removal in integrated mobileaudio/video system installations:

Center dash panels (surrounding headunits, HVAC controls, etc.)

Center console panels and complete center consoles


Glove boxes (and surrounding area)


Headrests

An integrated mobile A/V

system is more complex than a

simple rear seat entertainment

system.

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Door panels (front, rear, and cargo doors)


“A”, “B” and “C” pillar panels

Headliners

Rear side panels

Rear deck panels


Trunk cosmetic panels

Parts common for removal in rear seat entertainment system installationsinclude:



Headrests



“A”, “B” and “C” pillar panels

Headliners

Rear side panels


Though it is generally not necessary to entirely remove the floor carpet tofacilitate running wires in a rear seat entertainment system installation, correctly running the wires may necessitate seat belt and “B” pillar panelremoval as well as entire seat removal in some cases. This removal is almostcertainly necessary in an integrated mobile A/V system installation.

In vehicles with a trunk or under rear seat-mounted battery, always avoidrunning audio or video signal cables down the same side of the car as thebattery-to-alternator connection cable. This battery cable carries highcurrent and will almost certainly be a source for some kind of electromag-netic interference (EMI)-related noise problem. In video system installations,this can be especially troublesome with both audible and visual noise. Video noise results in fuzzy and poor picture quality. Using the appropriate75-ohm shielded video cable helps to avoid unnecessary video noise.

Another concern when choosing wiring paths in an integrated mobile A/Vsystem is the use of plastic optical fiber (POF) cabling connecting DVDplayers to Dolby Digital or DTS processors. This cable is impervious to EMI-related noise, but it does not tolerate sharp bends. You should thereforeavoid using it around any sharp surfaces or wire paths that create severebends in the cable.

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Margin Notes

Seat and seatbelt anchor

bolt removal is often a

necessary part of running

wires in a vehicle.


Avoid any sharp bends in a

POF cable used for discrete

multi-channel audio in an

integrated mobile A/V

system

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Most important in any vehicle disassembly-regardless of the mobile videoinstallation task-is to put back the original hardware for panel attachment as it was originally assembled from the factory. Often the easiest way for anautomotive mechanic to blame a video component installation for a vehicleelectrical problem stems from looking at the attention to detail given to cor-rect reassembly of the vehicle interior panels. To avoid damaging any panelclips, always use the appropriate panel removal tools, and always be aware ofwhere panels are stored while they are out of the vehicle. Laying a blanket orstrip of carpet across a storage shelf helps ensure that the panels will not getscratched while in your care. Also make sure to use two installers for anyheadliner removal, so you avoid any unnecessary bends or creases in the fac-tory headliner. There is nothing worse than handing the customer the keys,only to have him or her notice the big crease or dent in the felt headlinersurrounding the new video component.

Some of the methods by which interior dash and trim panels are removedfor installation and/or modification are covered in Chapter 2 of this MECPStudy Guide, “Advanced Installation Knowledge and Technique.”

Mobile Video Entertainment Systems VIDEO SOURCES

VHF/UHF TV TUNERSTV tuners have been offered for the mobile audio/video market since themid-1980s. Mobile tuners can be standalone units or incorporated into othermobile video products. In either case the tuner consists of the two maincomponents-the channel coverage and the antenna section. The channelcoverage includes local stations that broadcast their signal to surroundingareas. The stations operate on different frequency ranges. The ranges aresplit into two categories, VHF and UHF.

Very High Frequency (VHF). Refers to frequencies between 30 and 300MHz, which includes TV channels 2-13.

Ultra High Frequency (UHF). Refers to frequencies between 300 and3000 MHz, which includes channels 14-69.

The antenna section of the tuner brings in the signals over the air in thesame way your AM and FM radio functions.

Mobile TV antennas come in various shapes and sizes, and also differ forvarious applications. Fixed-mount boomerang antennas have been used inthe limousine and executive transportation market for years. In modern systems, many of the mobile TV antennas are window-mounted units, allow-ing for more mounting options without drawing additional attention to thevehicle. Some tuner packs have a diversity tuner that allows the installationof several antennas located away from each other, connected to a singlereceiver via an internal antenna switch. At regular intervals, the receiverstops receiving, looks at the antennas and selects the one with the best signal as the input.

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Margin Notes


If you must use a VHF/UHF

TV tuner in a vehicle, choose

diversity tuners with a dual or

quad diversity antenna for best

reception while on the move.

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Advantage of using TV tuners in mobile applications. TV tuners are an inexpensive way to receive local channels on a monitor. Since manymobile video monitors and VCPs have a tuner built in, it is a cost effec-tive alternative to more costly external video sources such as DVDs orvideo game consoles.

Disadvantages of using TV tuners in mobile applications. Because ofthe nature of using airwaves to receive the signal, many times the pic-ture and sound quality are less than adequate due to the fluctuation ofthe antenna ability to pick up the station’s signal. The FM band is locat-ed between channels 6 and 7 on VHF, and is closest to channel 6. A strong FM station might cause interference on channel 6 because of its close proximity. Most customers find mobile TV reception onlyadequate at best.

SATELLITE TELEVISIONSatellites are used for voice, data and TV communications worldwide.Signals are beamed from the uplink sites to the satellites, which then beamthe signal back down over a target area such as the United States, Canada or other parts of the world.

Most network and cable programs are transmitted on a series of C-bandsatellites and some Ku-band satellites. These two types of satellites use dif-ferent frequencies, much like VHF and UHF broadcast TV use different fre-quencies. Communications satellites were originally designed for sendingtelephone, radio, TV and other signals across the country and around theworld for re-transmission to businesses and homes by local telephone com-panies, TV stations or cable companies. Enterprising individuals soon builtsatellite dish receivers to pick up these signals at home, and began makingand selling these systems to homeowners, thus beginning the era of homesatellite TV. During the 1980s and early 1990s, several million of these C-band systems were sold with dishes generally around the 10’ diameter.

As home satellite systems became more popular, program providers such asHBO realized that they could not continue to give away their programs freeto millions of home dish owners. They developed a scrambling system sotheir signals were no longer broadcast in the clear for everyone with a dishto pick up without any payment to the program developers.

A few channels were broadcast on the higher frequency Ku-band satellites,and some hybrid C/Ku-band systems were sold. Ku reception never becamevery popular due to the difficulties in receiving the Ku channels and to thelack of sufficient programming on these satellites.

In 1994, the GM Hughes DIRECTV system launched using a newly designedhigh power Ku-band satellite and an 18” dish. This system provides a greatpicture and stereo sound on 150-200 video and audio channels, and made itpossible for the small dish era to begin in a serious way. In 1996, the Echo

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Star Dish Network system launched. Both systems (Direct TV and DishNetwork) use four main components: the uplink site, satellite, dish antennaand the receiver.

Common Satellite Terms:

TV Satellite - An electronic communications relay station orbiting22,237 miles above the equator, moving in a fixed orbit at the samespeed and direction as Earth (about 7,000 mph east to west). Satellitesrelay audio/video signals to your receiver, where information isunscrambled and converted.

Parabolic Dish - The most common satellite TV antenna, named forthe shape of the dish (a mathematical parabola). The parabolic shapefocuses the weak microwave signal, hitting the surface of the dish at asingle focal point where the communications pickup (also called theLNB) is usually located.

Satellite Receiver - The component that converts the digital satellitesignal to a signal displayed on your television screen. The receiver alsoallows you to change DSS channels.

To date, mobile applications for satellite television on the move are still veryfew. Often the most common mobile application is in RVs that travel to a des-tination, set up and calibrate the dish to the appropriate southern-facingcoordinates, and enjoy the satellite broadcast as long as the RV is parkedthere. To keep a dish aligned with the exact satellite signal while a vehicle isin motion along city streets and mountainous terrain is a challenge that hasyet to be overcome. Additional challenges are the physical size of the antennaon a moving vehicle and the DC-AC electrical conversion to power the satel-lite receiver in a 12-volt environment. Still, if a customer absolutely musthave a satellite system while on the move, solutions are currently available.

VHS TAPES (VCP, VCR)The VCR (video cassette recorder) or VCP (video cassette player) is one ofthe most popular home electronics products ever built. The VHS (videohome system) VCR has found its way into nearly every home in the country,and many homes have more than one. When video began in mobile applica-tions, VCPs were the most common and least expensive video source thatgave reliable, reasonably good picture quality without an antenna or movingreception.

A VCR or VCP can play movies from VHS tape. It can play back movies created on video camcorders, and VCRs can tape programs from televisionbroadcasts or other sources for later viewing. Even with all the advances indigital mobile video source units, the VHS format is still an essential elementof many mobile video entertainment systems.

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Even though the VHS VCR is common to many mobile and home video systems, its limitations will be apparent once a viewer has compared it todigital formats such as DVD-Video discs or HDTV broadcasts. The VHSimage quality is noticeably poor, due mainly to its limitations in resolution.VHS tape has a resolution of approximately 240 lines (horizontal), which isabout half the resolution the North American NTSC TV system can display.Newer formats take advantage of higher resolutions, for example 500 linesfor DVD-Video. This lack of resolution appears as softness in VHS imagedetails and bleeding of adjacent colors. The tape format itself is prone tonoise-disruptions in the purity of the signal-often described as “snow.”

S-VHS TAPESS-VHS was introduced in response to the criticism of the poor video qualityof standard VHS recordings. S-VHS is not just a buzzword, but an entirelydifferent system of recording video signals on VHS tapes. However, it hasnever become a widely accepted format for consumers, so it is a subject ofconfusion.

S-VHS records luminance and chrominance (BandW picture and color information, also called Y and C) separately, rather than as a composite signal. By doing this, the deck is able to record and play back a wider band-width, or a much higher resolution signal than a normal VHS deck. The signal is also output via a S-Video connector that also keeps the Y and C signals separate. The result is a much clearer, higher definition picture thanVHS. The horizontal resolution of S-VHS is around 400 lines, compared to240 lines of normal VHS in SP mode.

S-VHS is most often used by commercial or educational organizations. Theycan record video with an S-VHS camcorder at 400 lines and then edit it onS-VHS editing equipment. This allows editing with a very good signal. Evenafter making multiple copies, the final result is still higher than the qualityof broadcast television. With standard VHS, the end result would be notice-ably poor, even to an untrained eye.

Unfortunately, S-VHS rarely finds its way into mobile applications or homesbecause it is nearly impossible to find movies to rent in that format. Also, if you make your own recording on the required special S-VHS tapes, moststandard mobile VHS VCRs will not play them. Perhaps most important isthat DVD-Video is now widely available and getting more accessible to con-sumers each day.

DVD-VIDEODVD is an optical storage media format that is primarily used for playbackof movies with high video and sound quality. A DVD disc can be DVD-Video(containing movies), DVD-Audio (containing high-definition sound) andDVD-ROM (containing data). Many consumers and installers assume DVDstands for digital videodisc, which is merely one of many applications for the DVD media. But the “V” stands for versatile.

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Margin Notes

Many VHS players are

specifically engineered for

the mobile environment and

release the magnetized video

head from the tape when not

in play (even while power is

still on). This eliminates

unnecessary wear due to

moisture and vibration.


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A DVD can contain up to 150 minutes of video on a single side, allowingcontinuous playback of most feature-length movies. However, because some movies are longer, the only way to achieve continuous playback is tospread the movie and other contents over more than one layer within thesame side. DVDs that do this are known as dual-layered or RSDL (reversespiral dual layer). RSDL technology allows for more than three hours ofmaterial on a single side. This is desirable when a film is particularly long,or contains a wealth of extra materials, which can be accessed without having to flip the disc.

In addition to extra materials, certain DVDs contain both the full-frame andwidescreen versions on the same side. You can select the appropriate versionfrom the disc’s main menu. All of this is only possible with dual-layer tech-nology.

All DVD players can play dual-layered discs, which are identified by the goldtint of the playing side (the side that faces down in the player). The layertransition often occurs during the running time of the movie, at which pointyour player will pause (showing a still frame) for approximately 1-2 secondsand then continue playing. In certain cases, layer transitions occur as theimage fades to black, so there is no noticeable pause.

DVD-Video discs require a DVD-Video player, which is similar to a commonVCR, but cannot record onto the discs as standard. Commercial DVD moviesare encoded using a combination of MPEG-2 compressed video and DolbyAC-3 audio (often in multi-channel formats.) Typical data rates for DVDmovies range from 3-10 Mbps, and the bit rate is usually adaptive.

THE VIDEO PORTION OF A DVD-VIDEO DISC

MPEG-2 Video CompressionUsing a digital compression called MPEG-2, DVD can provide between 475 and 500 lines of visible resolution, more than double the resolution ofstandard mobile VHS players. This level of sharpness and clarity eliminatesvideo noise, and ensures deep blacks and vibrant colors. Like the CD, theDVD never wears out after repeated use. MPEG stands for Motion PictureExperts Group.

Anamorphic TransferAnother feature exclusive to DVD is the 16:9 anamorphic transfer, currentlyemployed by most of the major studios. Because most DVDs include bothfull-frame and widescreen versions, the viewer has a choice. Widescreenvideo monitors are 33 percent wider than regular televisions. Now thatwidescreen video monitors in the mobile environment are becoming moreprevalent, DVD’s digital technology is being used to produce widescreen versions that are not letterboxed but rather specially formatted to fitwidescreen televisions, thereby producing an image 33 percent sharper than standard DVD (16:9=1.78:1 just as 4:3=1.33:1). The aspect ratio ofwidescreen television is 16:9 (1.78:1), while regular television is 4:3 (1.33:1).

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The term “anamorphic” describes the fact that an image wider than a squarehas been squeezed into a square frame (a television screen, for example).Any film that has been made in an aspect ratio of 1.78 or wider can beanamorphically mastered to DVD, because this is the aspect ratio ofwidescreen televisions. Not all DVDs that are mastered in this format willmention it on the box, but those that do refer to this as “16X9 enhanced” or “enhanced for widescreen televisions.”

When producers letterbox a movie, they waste valuable screen space by taking up part of the screen with those black bars. With small screens in themobile environment, the black bars on a video screen can eat up valuableviewing space, making movie watching much harder for passengers. Bysqueezing the sides of the picture in, you would not have to letterbox thepicture-if there were a way to unsqueeze the picture later. You can do thiswith widescreen video monitor.

An anamorphic DVD squeezes the picture in on the sides, making it look tall and squished. When this is done to movies wider than 1.78, small blackbars still appear above and below the image, but this is necessary. BecauseDVD is a digital format, you still get all the benefits of anamorphic evenwith wider movies. If the installation has a widescreen video monitor, youcan unsqueeze this image to make it look normal on the screen. Becauseblack bars take little or none of the picture, more of the screen is used todisplay the image. As a result, the sharpness and detail increase by approxi-mately 33 percent.

If a widescreen video monitor is not present, the DVD player will automati-cally convert the image into a letterboxed picture. In this case the DVD player will generate the black bars, meaning that all the available resolutionwill be used to display the movie image and not the black bars. Therefore,no matter what size of screen is being installed into the vehicle, you canview both anamorphic and non-anamorphic DVDs with relative ease.

Aspect RatioThe term “aspect ratio” describes the degree to which an image is wider thanit is tall. Since movies are filmed wider than the video screen on which theywill eventually be displayed, letterboxing preserves the image with blackbars on the top and bottom. However, from movie to movie, the size of thebars will change. For example, the black bars on the letterboxed version ofJurassic Park are smaller than the black bars on the letterboxed version ofJaws, but both versions display the entire filmed image as it was released for the theater. This is because there are a number of widescreen processes,which determine how wide the movie image will be. The number to describean aspect ratio is read as width to height, the height always being 1.

1.33:1 - Also known as 4:3, this is the aspect ratio of a television screenand of standard 35mm film. Movies made before 1952 were mostlyfilmed in 1.33 and will transfer normally to video. Examples: Gone WithThe Wind, Citizen Kane and The Wizard Of Oz.

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1.85:1 - This is called standard, or flat, because it requires no speciallenses. Movies produced in this format are 33 percent wider than stan-dard televisions. All movie screens in North America have an aspectratio of at least 1.85:1. Examples: The Fugitive, Batman and Men In Black.

2.35:1 (Anamorphic) - This format produces an image that is nearlytwice as wide as it is high, and therefore it is also twice as wide as yourtelevision screen. Special lenses squeeze this image onto standard 35mmfilm and the same lenses produce a viewable image during theatricalprojection. This format is still widely in use for action/adventure andfantasy films, and is denoted by the appearance of the words“Cinemascope” or “Filmed in Panavision.” Other international formatswork the same way but under different names. Examples: Star Wars,Blade Runner and Heat.

70mm 2:1 - “Event” movies of yesteryear were often filmed in the70mm format, which uses a very large frame to capture extremely clear,grain-free images with a sweeping grandeur. Today, only a handful ofmovies are made in this format. The 2:1 aspect ratio falls between stan-dard flat and 2.35 anamorphic, and can be altered to appear closer to2.35 if the filmmaker desires. Examples: Lawrence of Arabia, Far AndAway and 2001: A Space Odyssey.

Super 35 2.35:1 - also known as Super Scope 235, this uses modified35mm film to produce a slightly wider image, with the director framingfor a 2.35:1 image within the Super 35 frame. This takes advantage ofthe fine quality of Super 35 lenses without dealing with the distortioninherent in anamorphic lenses, while still achieving the widescreenaspect ratio. Examples: Titanic, The Abyss and Terminator 2.

A note about IMAX: IMAX movies are actually photographed on 70mmfilm turned sideways, and as a result achieve a nearly square frame. Dueto the size of IMAX screens, it is not necessary for the format to bewidescreen, and this is why video transfers of IMAX material are not let-terboxed.

You may find that certain letterboxed movies deviate from these formats, butyou can be certain that no matter what the aspect ratio, a letterboxed editionlets you see what the filmmakers intend for you to see.

Another feature that is becoming widespread is the audio commentary,which first appeared on the laserdisc format. DVD is uniquely capable ofpresenting audio commentary in clear, digital sound with easy access to different scenes and audio tracks. The audio commentary is a chance for you to essentially watch the film with the voice of the director guiding youthrough the making of the movie. Never before has it been possible to preserve these valuable observations on the nature of filmmaking from theluminaries of the industry. Even a casual film fan can learn a lot. Sometimesthese audio commentaries are spiced up a bit by including some of the film’sstars along with the director. Some DVDs offer two or three separate runningaudio commentaries, allowing the director to have his say without beinginterrupted by other members of the filmmaking team who offer their own

DVD-V discs may feature

a screen aspect ratio that

appears squashed and

stretched when displayed on

some screens not configured

for adaptive aspect ratio

settings. Additionally,

widescreen DVD-Video disc

formats may appear to be

missing content on the sides

when displayed on standard

4:3 ratio screens.

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commentary on a separate track. Consider such a feature a seminar withfilmmaking greats, and you will undoubtedly come away with a deeperunderstanding of the creative process.

In addition to documentary footage, many DVDs contain deleted scenesand/or outtakes from the movie, which provide insight into the directionsthat the movie could have taken. Often, such scenes will feature a secondaryaudio track with commentary from the director explaining why that particu-lar scene was cut.

THE AUDIO PORTION OF A DVD-VIDEO DISC

Digital Audio Coding TechniquesThe audio data on a DVD movie can be in the format of PCM, DTS, MPEG-2audio or Dolby AC-3. In the NTSC countries (North America, Mexico,Canada and Japan), any DVD movie should contain a soundtrack in PCM or Dolby AC-3 format, and any NTSC player must support at least these twoformats. All the others are optional. This ensures any standard compatibleDVD-Video disc can be played on any standard compatible player.

PCM (Pulse Code Modulation)This audio format addresses the applications where a discrete or matrixedsurround sound application is not in place. PCM data is essentially 2-channel, just like most mobile audio source units. The difference is thatPCM audio is digital in nature. Remember the binary representation andconversion back into an analog waveform? PCM data requires a D/A conversion to create a traditional 2-channel RCA type analog audio output. Most mobile DVD players have this output option. Some less costly mobile models only have an analog RCA output with an internal,inexpensive PCM D/A converter.

Dolby Surround 2.0This sound format “matrixes” four channels of sound from a 2-channelstereo mix: center, left front, right front and rear channel. This differs fromDolby Digital in that the four channels are not full-range, and the rear chan-nel, which still requires two speakers, is a mono channel without directionaleffects. Dolby Surround can be very dynamic. Some DVDs will provide separate Dolby Surround and Dolby Digital soundtracks, so you can choosewhich one you would like to hear. Those DVDs that only provide a DolbyDigital soundtrack will still play normally through any stereo receiver or television because your DVD player will automatically convert the digitalmix to a matrix surround mix. DTS DVD-Video discs all contain a separateDolby Surround version.

Dolby Digital 5.1This means that the movie soundtrack is presented in full-range digital surround, with fully separate or discrete sound in five channels: left front,center, right front, left rear and right rear. The .1 indicates that there is afully separate bass channel for low-level sound, which feeds a subwoofer.

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This is often called the LFE channel (low frequency effects). The DolbyDigital format is encoded with AC-3, a universal format for Dolby Digitalsignals to transfer into and out of consumer audio/video equipment. AllDVD players can output a Dolby Digital/AC-3 encoded signal, but a DolbyDigital decoder/receiver is required to decode the signal and process it onthe receiving end. Because of Dolby Digital 5.1, older movies with 70mm 6-track split surround mixes or early digital sound mixes can now be presented on DVD with accurate discrete stereo sound.

DTS Digital 5.1 SurroundThe DTS (digital theater systems) version of discrete multi-channel audioencoding works similar to Dolby Digital but with a different bit rate, whichcan allow for subtle differences in the sound mix. Most DVD-Video playerscan output the DTS digital audio signal, but a DTS decoder/receiver isrequired to decode the signal and process it on the receiving end. Currentlymost DVD-Video discs with digital sound use Dolby Digital, but many DTSDVDs are available.

DTS-ES (Extended Surround)DTS-Extended Surround (ES) adds a center-surround channel to the existing5.1 channel array. DTS-ES is the only home format that can deliver all 6.1channels as discrete. DTS-ES is fully compatible with all types of multi-chan-nel systems. You will hear all sounds, whether played back as discrete,matrix or on a 5.1 mobile audio/video system. Currently, no mobile A/Vprocessors offer DTS-ES decoding for the automobile.

Older Mono SoundtracksNot all movies are in stereo. Older movies may be in mono, or 2-channelstereo without surround information. In these cases, Dolby Digital encodingmay be used to contain these versions. This means that not all DVDs that sayDolby Digital are actually in 5.1 surround. Dolby Digital is a digital soundstorage format, with the option to hear mono, stereo, matrix or 5.1 surrounddepending on how the movie was originally mixed. With the Dolby DigitalAC-3 perceptual coding, sampling rates of 32kHz, 44.1 kHz and 48kHz aresupported, while data rates range from as low as 32kb/s for a single monochannel to as high as 640 kb/s for multiple channels, thereby covering a widerange of requirements. Most important with blending old and new videoentertainment soundtrack formats, all Dolby Digital and DTS-encoded DVD-Video discs will sound normal no matter what sound system you use,provided the signal gets from the source unit to the amplifiers.

RMIC Regional Numbering SystemAll DVD titles are marked with a number, the regional management informa-tion code (RMIC), which appears in a globe on the disc cover. This numberindicates in which countries the DVD will play. Region 1 (NTSC) DVDs playin Canada and the United States only. There are a handful of DVDs that arecoded to all regions, but this is rare. Just as rare are DVD players that arecapable of playing DVDs from all regions, though some players with an

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To use the TosLink optical

digital output of a Dolby Digital

or DTS-encoded audio signal

on a DVD-Video player, you

must have a decoder or

processor with a digital input.

This typically features multiple

discrete outputs for the

amplifiers that support a

5.1 mobile surround system.

14683_CEA 2/10/04 6:52 PM Page 241

internal switch or a programming routine allow you to choose or enable the country code. Most likely the DVD player you install into a customer’svehicle will be coded only to the region in which the customer lives.

Region Areas

1 U.S., Canada

2 Europe, Middle East, Japan, South Africa

3 South Korea, Taiwan, Hong Kong, ASEAN

4 Australia, New Zealand, Latin America

5 Former Soviet Union countries, Indian sub-continent, Africa

6 China

7 Reserved

8 International territory (airplanes, cruise ships, etc.)

Video CDPhilips and Sony introduced video CD (VCD) in 1993. VCD, a digital movieformat, is basically a primitive version of DVD. A video CD looks the sameas a music CD or a CD-ROM, but it holds movies, using compressed MPEG-1 video. The resolution of a video CD is 352x240 (NTSC) or 352x288(PAL), which is roughly comparable to VHS.

Compared to video CD, DVD provides much higher resolution (700x480),comparable to laserdisc or even better. DVD movies use MPEG-2 compres-sion, rather than the MPEG-1 compression used by video CDs.

A single VCD disc can only hold about 70 minutes of video, so for a typicalmovie, you need two discs. You can play VCDs back on a video CD playerconnected to a TV, or on a fast PC with a CD-ROM drive. Most mobile DVDplayers can also play VCDs.

Video Game ConsolesA video game console is a dedicated electronic device used to play videogames. Often the output device is a separate television. Once video gameconsoles were easily distinguishable from personal computers: consoles useda standard television for display, and did not support PC accessories such askeyboards or modems. However, as consoles have become more powerful,the distinction has blurred. Some consoles can have a full Linux OS runningwith hard drives and keyboards. The console market has steadily developedfrom simple games, such as Pong, to full-featured games systems.

Sony PlayStationThe PlayStation is a video game console produced by Sony; it was launchedin Japan in December 1994 and in the U.S. in September 1995. It is impor-tant in the history of video games, being the first popular console to havethe power to do 3D graphics using its 33MHz custom CPU (MIPS R3000A).It was hugely popular and spawned a PlayStation generation. Sony nowmakes a compatible console in a smaller, curvier case called the PSOne.

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Margin Notes

Most mobile DVD-Video

players are backward

compatible with video CDs

and play them in addition to

other media such as music

CDs. Video CDs do not feature

Dolby Digital or DTS-encoded

audio, however.


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Sony’s successor to the PlayStation is the more powerful PlayStation 2, whichis compatible in the sense that it can play most PlayStation games unmodified.The most important parts of the PSOne are embedded inside the PlayStation2 design, so you get two systems for the price of one. The PS2 can read CDs,for playing audio CDs and original PlayStation games, and DVDs for DVD-Video and PS2 games. Its ability to play DVD movies was an important sellingpoint at a time when few people owned a separate DVD player. The PS2 hadmany features-including its USB and IEEE 1394 expansion ports-that werenot present in other video game consoles at the time.

Nintendo Game CubeGame Cube is Nintendo’s next-generation console. The Game Cube has beenwidely anticipated by many who were shocked by Nintendo’s decision todesign another cartridge-based system after their previous game system. The Game Cube uses a unique storage medium, a proprietary DVD format that holds 1.5 GB of data. The Game Cube does not have any DVD movie support.

Microsoft X-BOXThe X-BOX is Microsoft’s game console, released in November 2001. It isMicrosoft’s first venture into the console market. Microsoft’s X-BOX is basically a stripped-down PC running a version of Microsoft Windows that allows for robust graphics and fast processing of interactive gamingcommands. Of all the gaming systems, the X-BOX has the fastest processingspeed, but still does not have the game availability of other, more established game systems.

DC-AC Power Inverters Virtually all 110v gaming systems require a DC-AC power inverter to operatein the vehicle. A power inverter connects to +12v and chassis ground (like an amplifier) and provides a 110v, 60Hz AC output sufficient to powerdevices that fall within its power rating limits. In most cases a DC-AC powerinverter has one or more electrical outlets so the AC device just plugs in.

It is important to note that power inverters are available in many shapes andsizes, both physically and electrically. Power inverters are very much likepower amplifiers in that larger capacity inverters require larger gauge cablingand more attention to heat dissipation, just as large power amplifiers do.

The need for heat dissipation and the length of the power cords on the ACdevices typically dictate installation location of the DC-AC power inverter.While there is no hard and fast rule about the installation, here are a fewguidelines:

1) Provide adequate airflow. Install the DC-AC power inverter in a location that provides adequate air circulation. Larger capacity invertersneed more attention then small capacity inverters do. As a rule ofthumb, provide the same air circulation to a DC-AC power inverter that you would to a mobile audio power amplifier.

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2) Keep away from sensitive audio cables/components. Install the DC-ACpower inverter in a location away from sensitive preamp level audiocables or preamp level signal processing components. The oscillation ofthe 60Hz frequency may superimpose a low frequency hum on the lowsignal levels in preamp level components.

3) Connect directly to the battery. Connect a DC-AC inverter directly tothe battery. If no power switch is provided, use a relay to activate theconnection whenever the inverter will be used. Remember that tradi-tional Bosch-type SPDT relays have a reliable switching current of 30amps through the contacts, so if the current requirement on the powerinverter exceeds that, choose a higher current relay.

4) Avoid modifications. Whenever possible, avoid modifications to a DC-AC power inverter if it needs to be removed for a warranty repair. Anymodification, external or internal, typically voids any warranty. If youdo make modifications, assume that any warranty on the device is void.Additionally, only a qualified professional installer should perform anymodifications.

Video Output Formats COMPOSITE VIDEO OUTPUT (YELLOW RCA PLUG)Composite video signals are connected between products with a single 75-ohm coax cable, usually with yellow RCA connectors on each end.Composite video inputs or outputs are present on almost all contemporarymobile video equipment. Composite video signals can also be modulatedonto an RF carrier, along with an audio signal, and transmitted over-the-airor on coax cable, by broadcast stations and cable TV systems. RF video sig-nal cables are usually 75-ohm coax terminated with screw-on F-connectors,such as those found on some mobile VCR/VCP and TV tuner inputs.

Picture Quality: Good

This is the lowest quality cable for a video source, but again, it is alsothe most common. Most mobile video products support the compositevideo input and/or output format because it is easy and only requiresone simple cable to connect between a video source and screen.

S-VIDEOMost mid-range and premium home video equipment provides the option of using S-video connections. The S-video (or Y/C) cable terminates at eachend with a four-pin DIN connector. Although it may appear to be a singlecable, internally it has two 75-ohm coax or twisted pair cables to carry theseparate Y (luminance) and C (chrominance) signals. Many companies offeran in-dash video monitor with a hideaway sub-chassis that holds the actualvideo processing circuitry. This kind of monitor uses a modified S-video connection (with its own proprietary cable) between the in-dash unit andthe sub-chassis.

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Margin Notes

The composite video

output is the yellow RCA

connector on most video

source components.


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Picture Quality: Better

The S-video cable offers marked improvement over a composite cable.Few if any applications of mobile video products use commercial S-Video input and output formats. Almost all aftermarket mobile video LCD monitors accept only composite video inputs.

COMPONENT VIDEO (RGB)Component cables look just like composite cables, but where a compositecable carries the entire video signal on a single cable, component cables splitthe signal in three. The signal itself is either Y, Cr, Cb or Y, Pb, Pr. Mostmanufacturers make connecting these cables easy by color coordinatingthem. The tips of the cables and jacks are red, green and blue. Unfortunately,this can be a bit confusing because computer RGB connections are coloredthe same way.

A good rule of thumb is that if the connections are the RCA type, the cableis usually a component cable. Computer RGB cables will usually be BNCtype. Most high-end home DVD players and HDTV tuners will have compo-nent connections. Sadly, component video applications almost are neverfound in the mobile environment due to manufacturing cost increases tosupport the component video format. Small screen sizes in the mobile environment make it difficult to recognize enough difference to justifyincreases in product costs.

Picture Quality: Best

This connection gives a superior image over composite or S-video con-nections. Unfortunately, it is almost never seen in dedicated mobilevideo products due to manufacturing expense versus measurable resultsto the consumer. Due to the small screens in mobile applications, muchof the component video resolution would go unnoticed.

NTSC, PAL and SECAM Video StandardsThree major TV standards are used in the world today: the American NTSCcolor television system, the European PAL and the French-former SovietUnion SECAM. The largest difference among the systems is the verticallines. NTSC uses 525 lines (interlaced) while both PAL and SECAM use 625 lines. NTSC frame rates are slightly less than half the 60 Hz powerlinefrequency, while PAL and SECAM frame rates are exactly half the 50 Hzpowerline frequency.

NTSCNTSC stands for National Television System Committee, the video transmis-sion standard for North and Central America and Japan. It was developed inthe U.S. as the world’s first color TV system and first broadcast in 1954. Itstechnical format has a fixed vertical resolution of 525 horizontal linesstacked on top of each other, with varying numbers of lines making up thehorizontal resolution, depending on the electronics and formats involvedwith roughly 30 fps (frames per second) refresh rate.

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Basic parameters NTSC

Line/field 525/59.94

Horizontal frequency 15.734 kHz

Vertical frequency 60 Hz

Color sub carrier frequency 3.579545 MHz

Video bandwidth 4.2 MHz

Audio carrier 4.5 MHz (FM)

Advantages of NTSC Higher Frame Rate - Use of 30 frames per second (really 29.97)reduces visible flicker.

Atomic Color Edits - With NTSC it is possible to edit at any 4-fieldboundary point without disturbing the color signal.

Less Inherent Picture Noise - Almost all pieces of video equipmentachieve better signal-to-noise characteristics in their NTSC form than intheir PAL form.

Disadvantages of NTSC Lower Number of Scan Lines - Reduced clarity on large screen TVs;line structure more visible.

Smaller Luminance Signal Bandwidth - Due to the placing of the color sub-carrier at 3.58MHz, picture defects such as cross-color and dot interference become more pronounced. This is because of thegreater likelihood of interaction with the monochrome picture signal atthe lower sub-carrier frequency.

Susceptibility to Hue Fluctuation - Variations in the color sub-carrierphase cause shifts in the displayed color, requiring that the TV receiversbe equipped with a hue adjustment to compensate.

Lower Gamma Ratio - The gamma value for NTSC/525 is set at 2.2 as opposed to the 2.8 defined for PAL/625. This means that PAL/625 canproduce pictures of greater contrast.

Undesirable Automatic Features - Many NTSC TV receivers feature anauto-tint circuit to make hue fluctuations less visible to uncritical view-ers. This circuit changes all colors approximating flesh tone into a “stan-dard” flesh tone, thus hiding the effects of hue fluctuation. This meansthat a certain range of color shades cannot be displayed correctly. Up-market models often have this switchable feature, whereas cheaper setsdo not.

PALPAL stands for phase alteration line and was adopted in 1967 as theEuropean counterpart to the NTSC standard. It has 625 horizontal linesmaking up the vertical resolution and displays 50 fields interlaced per

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second, making for a 25 frame per second system. It is the standard for theUnited Kingdom, Western Europe (except France), the Middle East andparts of Africa and South America.

Basic parameters PAL

Line/field 625/50


Vertical frequency 50 Hz - 60Hz

Color sub carrier frequency 3.575611 MHz - 4.433618 MHz

Video bandwidth 4.2 MHz - 6.0 Hz

Audio carrier 4.5 MHz (FM) - 6.0 Hz (FM)

Advantages of PAL Greater Number of Scan Lines - more picture detail.

Wider Luminance Signal Bandwidth - The placing of the color sub-carrier at 4.43MHz allows a larger bandwidth of monochrome informa-tion to be reproduced than with NTSC/525.

Stable Hues - Due to reversal of sub-carrier phase on alternate lines,any phase error will be corrected by an equal and opposite error on thenext line. In early PAL implementations it was left to the low resolutionof the human eye’s color abilities to provide the averaging effect.

Higher Gamma Ratio - The gamma value for PAL/625 is set at 2.8 asopposed to 2.2 on NTSC/525. This permits a higher level of contrastthan on NTSC/525 signals. This is particularly noticeable when usingmulti-standard equipment, since the contrast and brightness settingsneed to be changed to give a similar look to signals of the two formats.

Disadvantages of PAL More Flicker - Due to the lower frame rate, flicker is more noticeableon PAL/625 transmissions, particularly for people used to viewingNTSC/525 signals.

Lower Signal to Noise Ratio - The higher bandwidth requirementscause PAL/625 equipment to have slightly worse signal-to-noise per-formance than its equivalent NTSC/525 version.

Loss of Color Editing Accuracy - Due to the alternation of the phaseof the color signal, the phase and the color signal only reach a commonpoint once every 8 fields/4 frames. This means that edits can only beperformed to an accuracy of +/- 4 frames (8 fields).

Variable Color Saturation - Since PAL achieves accurate color throughcanceling out phase differences between the two signals, the act of can-celing out errors can reduce the color saturation while holding the huestable. Fortunately, the human eye is far less sensitive to saturation vari-ations than to hue variations, so this is the lesser of two evils.

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SECAMSECAM stands for Systeme Electronique Couleur Avec Memoire, which wasadopted in 1967 and is very similar to PAL. It specifies the same number ofscan lines (625) and frames per second (25), but the chrominance (color) isFM modulated. It is the broadcast standard for France, Russia and parts ofAfrica and Eastern Europe with French influence.

Basic Parameters SECAM

Line/field 625/50


Vertical frequency 50 Hz - 60Hz

Video bandwidth 5.0 MHz - 6.0 Hz

Audio carrier 5.5 MHz (AM) - 6.5 Hz (AM)

Advantages of SECAM Stable Hues and Constant Saturation - SECAM shares with PAL theability to render images with the correct hue, and goes a step further inensuring consistent saturation of color as well.

Higher Number of Scan Lines - SECAM shares with PAL/625 a highernumber of scan lines than NTSC/525.

Disadvantages of SECAM Greater Flicker - Same as PAL/625 transmissions; particularly so forpeople used to viewing NTSC/525 signals.

Mixing Synchronous SECAM Color Signals Impossible - Most TV stu-dios in SECAM countries originate in PAL and transcode before broad-casting. More advanced home systems such as SuperVHS, Hi-8 andlaserdisc work internally in PAL and transcode on replay in SECAMmarket models.

Patterning Effects - The FM sub carrier causes patterning effects evenon non-colored objects.

Lower Monochrome Bandwidth - Due to one of the two color sub-carriers being at 4.25MHz (in the French version), a lower bandwidth ofmonochrome signal can be carried.

Incompatibility between different versions of SECAM - SECAM has arange of variants, many of which are incompatible with each other. Forexample French SECAM uses FM sub-carrier and MESECAM uses AMsub-carrier.

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Basic Elements of a Video System Installation Video SourceMobile video systems incorporate at least one video source component, most often a VHS or DVD-Video player. Though many in-dash units featureDVD-Video playback, the majority of mobile video systems rely on a sepa-rate video source component mounted elsewhere in the vehicle. Manymobile video systems use more than one source component. For example, a video system may contain a VHS player, DVD-Video player, CD/DVDchanger, TV tuner or video game console. These video sources must all have a manageable format in which to interconnect with the video screen(s).Often such a system can be challenging to install in a way that is easy for the customer to use and enjoy.

When selecting mounting locations, consider accessibility to video sourcecomponents. Because of their somewhat large dimensions, most video source components are not intended to be mounted in the dashboard (with the exception of DIN-sized DVD-Video headunits). Locations thatoffer accessibility and convenience also must not infringe upon the vehicle’snormal safe operation. Typically video source components are mounted inthese locations:

Under the front seats (if space allows) - TV tuner packs and hide-away sub-chassis are often able to fit under seats. Larger componentssuch as DVD-Video players, DC/DVD changers, VHS players and videogame consoles may only fit under front seats in large SUVs, trucks andmini-vans. Consider elevating any video source component off of thefloor so that it will not be damaged in case a beverage spills.

Under the middle or rear seats in SUVs and mini-vans - This is a logical place for video source components in most installations.Remember to install the source component so that a passenger can easily load and unload a disc or tape.

In the center console - Many components can be effectively mountedin a center console and accessed when needed, yet sit safely out of sightwhile not in use or when a movie gets underway.

In the trunk - The trunk is not ideal for single play video source components because it is hard to get to while traveling, but sometimesthere may be few other choices. Trunk mounting is suitable for aCD/DVD-Video changer since passengers control them from within thevehicle. Depending on the number of discs the changer accommodates,there is no need to get out of the vehicle to rotate disc selections.

In the glove box - Though this mounting location is less likely withbulky components, some glove boxes are spacious enough to conve-niently accommodate a video source component. Additionally, manymini-vans and SUVs have additional storage spaces throughout the vehicle where a video source component might fit.

A video source component

can often be controlled by a

wireless remote through the

use of an IR repeater.

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The majority of locations that are not directly accessible in the dashboardarea will require some method of control other than physically pushing but-tons on the unit. Most video source components have the option for aninfrared (IR) remote control and the IR receiver can extend so that is moreconvenient for those passengers commanding the equipment. This IR exten-sion is called an IR repeater and is commonly placed in the dashboard, cen-ter console or overhead console. Overhead and headrest screens may alsohave an IR repeater to increase the flexibility of operating the video system.Customers routinely point a remote control at the screen, even though thecomponent they want to control is mounted elsewhere. Take these facts intoconsideration when selecting a location for the IR controls if they are notalready built into the headunit itself.

VIDEO SCREEN TYPES

CRT (Cathode Ray Tube)A cathode ray tube (CRT, or picture tube) is a specialized vacuum tube inwhich images are created when an electron beam scans across the back sideof a phosphor-coated screen. Each time the beam makes a pass across thescreen, it lights up a horizontal line of phosphor dots on the inside of theglass tube. By rapidly drawing hundreds of these lines from the top to thebottom of the screen, it creates images.

CRT screens in the mobile environment are losing popularity for several reasons. They are heavy and difficult to secure, sensitive to vibrations, andhave extremely deep installation requirements that do not generally allowdash, headrest or console mounting. Some console applications accommo-date CRTs in custom floor or overhead van conversion installations. CRTsare also a popular choice for RVs that have generous space for both theweight and depth requirement of the screen.

Many CRTs used in 12v DC automotive applications have integratedVHF/UHF television tuners.

LCD (Liquid Crystal Display)Liquid crystal display technology is one of the methods used to create flat-panel video screens. Light is not created by the liquid crystals; a light source(bulb) behind the panel shines light through the display. The display con-sists of two polarizing transparent panels, called electrodes, and an electri-cally reactive liquid crystal solution sandwiched in between. An electric cur-rent passed through the liquid causes the crystals to align so that light can-not pass through them. Each crystal acts like a shutter, either allowing lightto pass through or blocking the light. The pattern of transparent and darkcrystals forms the image.

Thin film transistor (TFT) is the prevalent technology for building the LCDscreens for desktop displays, laptops and some high-end mobile video products. TFT screens are brighter and more readable than dual-scan LCD screens but consume more power and are generally more expensive.

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In general, more expensive components, such as in-dash retractable videoscreens integrated with a headunit, feature TFT screens because the cost canbe justified along with other features of the component.

Due to superior LCD sharpness, smaller screens look better at higher resolu-tions than CRTs can comfortably display. With LCD screens, the optimumresolution is termed the “native resolution.” The native resolution definesthe optimum resolution of the LCD and dictates that any other resolutionmay not be compatible. The luminance, or brightness, of LCD panels is alsoan important specification that indicates picture quality. Luminance is meas-ured in candelas per square meter (cd/m2, otherwise known as nits). This isnot an easy number to find, but it is worth digging up on a manufacturer’swebsite since more nits generally mean a more pleasing image, particularlyin difficult lighting conditions common to mobile video systems. The rangestretches from around 170 nits for an inexpensive LCD panel to around 300 nits for the best LCD panel (nearly equal to a bright CRT).

Another important consideration for viewing an LCD screen is the horizontaland vertical viewing angles. In the mobile video environment, approximateviewing angles should be at least 120° horizontal and 100° vertical. About thewidest available on a mobile video LCD screen is 160° for both horizontaland vertical viewing angles.

Comparison of CRT and LCDWith LCD monitors, there is a limit on colors, typically 16.7 million (alsoknown as 24-bit color). CRTs have no such limit, which in itself is no bigdeal since few applications go beyond 24-bit color. The real difference is incolor accuracy, a quality not reflected in manufacturer specs. CRT monitorsfar outperform LCD monitors when it comes to color. LCDs use magneticfields to twist particles floating in a liquid, which is an inherently less pre-cise process than the variable intensity electron beams of CRTs.

LCDs are slower than CRTs. Typically, it takes 20-50 milliseconds (ms) foran LCD pixel to respond, while it takes a CRT 8-12ms. The difference showsup in DVD movies, where fast-moving objects (particularly dark objectsacross a light background) may leave a slight trail of ghost images on anLCD.

LCD panels draw less than half the electrical power a CRT does. This is aconcern when several screens are in use within the vehicle, since the videosystem often plays with the engine not running for extended periods of time.

Perhaps the biggest consideration is the installation-friendly depth of LCDs,along with more affordable pricing. The installation flexibility of the LCDscreen makes it the clear choice for nearly every video system installation.

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Source Control MethodThe method by which the video and/or audio source(s) are controlled isimportant to consider as you are installing and/or integrating video sourcecomponents. Many devices have direct front panel control from a dash orconsole location while others require a separate controller, either wired orwireless, to perform control functions. Whatever the method, it is importantto make it easy for the driver or passengers to operate. Avoid the situation,such as in many home theater systems, where multiple remote controls arenecessary to operate each individual device. That gets clumsy and danger-ous. The system must be easy and intuitive for the customer to operate.

When wireless remotes are part of the source control method, many deviceswill be mounted out of sight and require an IR repeater installed in a location that makes it sensible for normal operation of the video source. For example, if a DVD player is trunk-mounted, the IR repeater should beinstalled on the dash, overhead console or center console so that the usercan easily point the remote at the device. It would be inconvenient andunsafe to require customers to point a remote under a seat or behind them toward the component.

Several mobile video products offer touch screen control directly on the front panel of the screen. While this is a useful feature for control, manyapplications for this function require the use of that particular manufacturer’sequipment as the both the source and video display components. In otherwords, touch screen control of a la carte video devices is not a turnkey optionwith current technology and product compatibility.

AUX INPUTS AND OUTPUTSMany video source components, particularly mobile VCs and VCPs, offeradditional inputs so that another video component can plug in, pass throughand go on to the main video source input of the system. This offers a con-venient way to add an additional component with no additional switcher or circuitry.

Just about all self-contained A/V products with a source component andvideo screen offer an additional audio and video output. Examples includeDIN-sized DVD players with a motorized flip-up screen, DVD overhead LCD consoles, DVD or VCP in a traveling bag or backpack and personalDVD players.

The audio output is necessary because few applications perform well with abuilt-in speaker in the chassis of an LCD monitor. Also, the additional audiooutput offers compatibility with amplification as well as external wirelessheadphone transmitters. The video output is almost a composite video out-put in the mobile environment and sends a video signal to any additionalscreens in the system.

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Margin Notes

Touch screen control

capability of video source

components is generally

manufacturer-specific and

not widely available for

systems with a mix of

brands.


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If the AUX inputs and outputs on a self-contained video device are usedproperly, operation of multiple A/V sources becomes easy and intuitive. Be sure to explain the control and switching methods to the customer upondelivery of the vehicle.

OEM Audio Integration with a Video SystemInstallation FM Audio Signal into an OEM HeadunitThe easiest method for getting an audio signal generated by a video compo-nent (such as a VCP or DVD player) into an OEM audio system is by FMmodulation. The FM modulator, widely available in many forms, has inher-ent drawbacks in channel separation and frequency response. If the OEMaudio system is otherwise stock, using an FM modulator is an option. Themajority of rear seat entertainment systems that have headphones are suit-able for implementing an FM modulator if the customer wishes to play the audio portion of the video source through the speakers.

With the FM modulator, only the audio is provided to the OEM headunit,therefore the headunit can only control volume. For the FM modulator tooperate properly, the appropriate FM station must also be selected. Thevideo source component still needs its own method of control for functions such as play, pause, stop, etc.

Auxiliary Preamp Inputs on an OEM Headunit (CD Changer Plug)Often CD changer plugs on an OEM headunit offer an audio input normallyused by the CD changer. If the changer is not present, there may be anadapter that plugs into this output to allow the audio signal from the videocomponent to pass into the preamp section of the OEM headunit and provide better sound quality.

If a changer is present, a skilled professional installer may be able to inter-rupt the audio input from the changer and switch to an alternative sourcecomponent, such as an aftermarket DVD player. An audio switching devicewill be necessary.

In either case, only the audio is provided to the OEM headunit, therefore theheadunit can only control volume. The video source component still needsits own method of control for functions such as play, pause, stop, etc.

Auxiliary Preamp Inputs on a Signal ProcessorWhen an external signal processor is used with an OEM audio system, a second set of inputs may be suitable for the addition of an additionalsource component. The in-dash signal processors such as equalizers and preamplifiers typically feature such an input. Since these are preamp leveldevices, a line output converter (LOC) also will be necessary for the OEMheadunit in most cases. Switching control between sources occurs on thefront panel of the in-dash signal processor.

FM modulation is an easy

and cost-effective solution for

getting audio from a video

source component into the

OEM audio system.

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When using a second input on a preamp level signal processor, only theaudio is provided to the signal processor, therefore only volume and sourceselection can be controlled by the processor. The video source componentstill needs its own method of control for functions such as play, pause, stop, etc.

External Switching System InterfacesSome specialty devices from third-party interface manufacturers may providea customized solution on certain vehicles. Additionally, if schematics for thepreamp loop inputs are available, a skilled installer can construct his or herown switching interface using a 4-pole double throw relay (or 4 SPDTrelays) and spike suppression diodes to minimize unnecessary pops whenswitching sources. The installer also may need to create the trigger for theOEM headunit to go to an AUX mode. Other solid-state switching applica-tions are possible as well, however each solution depends on the vehicle and the installer’s skill level. An installation shop could quite literally charge whatever the market will bear for these types of advanced level OEM integration applications.

Infrared and RF Wireless Headphone SystemsMany vehicles with stock OEM audio systems getting a rear seat entertain-ment system will never have any connection between the two. These sys-tems are often intended to operate independently of one another so that rearseat passengers can enjoy a completely different source than those seated inthe front. This is best accomplished by using wireless headphones. Wirelessheadphones offer the flexibility to be used virtually anywhere in the vehicleand to receive the audio broadcast for the corresponding video displayed onthe screen(s) in the rear seat entertainment system.

Wireless headphones operate by two basic methods. One is radio frequency(RF) and the other is infrared (IR). The main difference is that IR requires a“line of sight” between the transmitter and the headphones themselves.Though this is not usually a problem in the traditional vehicle, motor homesand buses may find limitations. Many video devices intended for installationin the headliner of the headrest provide an integrated IR transmitter toenhance the coverage of the infrared line of sight. Whenever installing astand-alone IR transmitter, always locate it in an overhead location. such asthe headliner or overhead console, so that it transmits the best possible lineof sight to the headphones.

RF-based headphones do not have the line of sight limitations of IR head-phones, but like anything operating on radio frequencies, there is always thepossibility of RF interference nearby. Mobile phones, AM/FM tuners, satelliteradio tuners, FM modulators, LAN devices and even switching amplifiersmay present interference. The newest RF headphone technologies offerbroadcast in very high bands to minimize RF interference in many newproducts.

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IR headphones are

“line of sight” so the

transmitter must “see”

the headphones for the

best results in various

seating and ambient

lighting conditions.


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Video Signal and Power Cabling Video Noise and InterferenceVideo noise? It seems as though noise should be “audible” rather than “visi-ble,” but the fact is that any type of signal in any frequency range is suscep-tible to noise. Video noise is identified by scrambled video imaging on thescreen, unnecessary lines, ghosting of the images, color problems and so on.Just like any other type of noise superimposed on to a pure signal, videonoise is unwanted. Although the source and screen components have some-thing to do with the video quality, cables that interconnect video devices areequally important. The same cautions that exist for audio cables apply tovideo cables. In fact, because video content is at much higher frequencies,shielding in video cabling is even more important than in audio cabling.

Remember that audio frequency ranges extend only to 20kHz (or 50kHzwith DVD-Audio) but video frequencies extend into the megahertz ranges.1Mhz is 1,000 times more than 1kHz. As frequencies increase into the mega-hertz bandwidth, shielding becomes more important in signal cabling.

75 ohm Coaxial CableComposite video signals are transmitted over a single cable. To maintain thepurity of this video transmission, use impedance-matched coaxial-shieldedcable suited for video frequencies. The appropriate type of cable is 75-ohmcoaxial cable with a braided outer shield. The term “75 ohm” means that thecable has an impedance of about 75 ohms between the center conductor andthe braided shield within the video bandwidth. This allows the appropriateimpedance-matching of composite video outputs from a DVD or VCP toplug into a composite input on a video display device, such as an overheadLCD screen. The cable will not measure 75 ohms of DC resistance betweenthe center conductor and the braided shield just lying on a bench. That iswhere the term “impedance” comes in. Impedance denotes a frequency-spe-cific resistance, which means that a video frequency must be applied whilethe cable is connected to the appropriate devices.

For the best results on video system installations, be sure to use 75-ohmvideo cables when connecting video source components to switchers, signalboosters and video screens. Avoid using standard audio RCA cables to con-nect video devices since there is a potential for unwanted video noise. Thelonger the cable run and the more screens in the system, the more potentialthere is for video noise and interference, especially when the incorrect cablesare used.

Video Signal AmplifiersA video output will not drive an unlimited number of video screens. Atsome point the video image quality suffers and continuing to add screensonly makes the problem worse. When many screens are used in a video sys-tem all fed by a single composite video output, there may be times when you

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need to amplify video signals. This is accomplished by one of two types ofsignal splitters:

Passive Video Signal Isolation - Passive splitters are small, transformer-based video signal splitters that essentially isolate each output becausethe input drives a primary transformer winding and each output is con-nected to a secondary winding. This is known as inductive coupling.The passive video signal splitter helps to avoid small video signal prob-lems, but it will not increase the signal strength. A passive device onlyprovides isolation.

Active Video Signal Boosters - Active boosters work much the same wayas line drivers work in audio systems for weak preamp level audio out-puts. To increase the signal strength of a composite video signal intoseveral screens, an active video signal booster is often necessary. Theactive signal booster has power connections to drive the amplification in the device, whereas a passive device only has video RCA jacks and no power connections. By increasing the video signal’s amplitude, thedevice can adequately drive each video screen. Most video devices out-put a 1-volt peak-to-peak video signal, so most screens have a maximuminput of 1-volt peak-to-peak. The video signal booster optimizes eachoutput to the 1-volt peak-to-peak signal.

Many switching and multi-source, multi-zone video devices have active sig-nal boosters built in to maintain optimum video signal strength.

Video Component Mounting ConsiderationsThere are many points to consider when choosing and implementing videocomponent locations. Perhaps the most important point is that placementmust be safe for both the driver and other occupants. Also, video sourcecomponents should be in convenient places and screens should be easy to view.

Choosing a Mounting Location for the ScreenThere are many choices for locating a single screen in a video install. Oncethe system increases to multiple screens, the choices change based uponhow the occupants intend to use the video coverage. What is most impor-tant is safety for the occupants. The viewing angle and resistance to glarefrom sunlight are important as well. Due to the relatively small size ofmobile video screens (compared to video displays at home), the distancefrom the mounting location to the occupant(s) is also a consideration.Ideally, the detail of the screen image, including colors and subtitles, shouldalways be visible.

In large vehicles such as Chevrolet Suburbans, Ford Excursions and mini-vans, several screens may be necessary to provide adequate viewing for allrows of seating. (Think of the many screens necessary to serve the numberof seats and passengers on a commercial airline.) Each overhead LCD screen

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covers just three or four rows of seating.) In a vehicle, a single overheadscreen supplemented by individual monitors further back in rear seat head-rests may provide the best results. Of course (if budget allows) the optimumplacement is one screen for each occupant behind the driver.

Many companies offer LCD screens that are application-specific (or haveapplication-specific mounting kits available) so that the screen(s) can beinstalled with a fit and finish that appears factory-installed. Though these aretypically more expensive for the customer, the installation time is much lessthan when the installer must create screens must have mounting provisions.An additional benefit of application-specific LCD screens is that they oftenare perfectly matched in color and texture to the original interior panels.Application-specific LCD screens are available (depending on the applica-tion) for overhead locations, headrest locations, sun visor locations and center console locations. Installers with limited experience in custom fabrication may find that application-specific video screens offer an effective solution to achieve the intended results.

Although video installations will be unique in each application, some common sense guidelines guide overall installation:

If there is only one screen, it will make the most sense to install it in acentral location from which everyone behind the driver can see it. The flipdown overhead screen is the most popular choice; be sure to choose one thathas a good screen image from a wide range of viewing angles.

When you install headrest screens, be sure to mount them so that curiouschildren or thieves cannot easily remove them. Safety is a prime concern forheadrest or seat back mounting locations. In an accident, the screen canbecome airborne and injure an occupant, so never rely on hot glue, pressurefitting or Velcro as the primary mounting method for a headrest- or seatback-mounted video screen.

When installing headrest screens, choose a screen with an extended lip or flange surrounding the screen housing so that the screen and the OEMheadrest upholstery blend together. The extended flange allows the OEMtrim material to terminate under the screen housing and provides a finishedlook. Of course if the installer can implement custom upholstery services,there are many opportunities to flush mount or rear mount the screen with a trim ring that the OEM upholstery wraps into. Keep in mind that any custom upholstery modifications should allow the screen to be removed forservice or repair if necessary.

Raw LCD screens may not indicate which way is up. Where raw screensare used with no mounting provisions, make sure the screen is not installedupside down in the headrest by connecting a test video signal before the finalinstallation. Once again, solid and safe mounting is especially importantwith these screens, largely because little, if any, mounting provisions are provided. These screens are typically the most labor-intensive screens toinstall in mobile video.

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Whenever installing a CRT screen (either in a center console or in anoverhead location for RVs and vans), always securely mount the screen. Inan accident, the CRT screen can fly around inside the vehicle, causing seri-ous injury to the occupants. In addition, the breaking glass from a CRTscreen can cause injury as well, so consider a location that is not directly atthe occupants’ face level.

Where governed by law, absolutely, positively do not install video screenswhere they will be in view of the driver while the vehicle is in motion. If the video screen is contained in a dash-mounted location, be certain to connect all of the safety precautions (such as the foot and parking brakeinputs) so that the entertainment video signals are disabled from the view of the driver while the vehicle is in motion. Generally, navigation systemsremain operable and the driver can see them while the vehicle is in motion.Entertainment screens (such as DVD, VHS, TV tuners, etc.) are disabledwhile the vehicle is in motion, although other screens behind the driverremain enabled for other occupants. This requirement may not agree with an installer’s personal tastes, but the legal liabilities to do otherwise-for both the shop and the installer-are much too great to ignore.

Video Screen Mounting Restrictions (By State)

State Restriction (*Exemption for navigation)

Alabama Not visible to driver

Arizona Not visible or located in front

Arkansas No laws

California Not visible or located in front

Colorado Not visible or located in front

Connecticut Not visible to driver

Delaware No laws

District of Columbia Not visible to driver

Florida Not visible to driver*

Georgia No laws

Hawaii No laws

Idaho No laws

Illinois Not visible to driver

Indiana Not visible to driver

Iowa No laws

Kansas Not visible to driver*

Kentucky No laws

Louisiana Not visible or located in front

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State Restriction (*Exemption for navigation)

Maine Not visible to driver

Maryland Not visible or located in front

Massachusetts Not visible or located in front

Michigan Not visible to driver

Minnesota Not visible or located in front

Mississippi No laws

Missouri No laws

Montana No laws

Nebraska Not visible to driver

Nevada Not visible to driver

New Hampshire Not visible or located in front

New Jersey Not visible to driver

New Mexico Not visible to driver

New York Not visible to driver

North Dakota No laws

North Carolina Not visible or located in front

Ohio No laws

Oklahoma Not visible to driver

Oregon Not visible or located in front

Pennsylvania Not visible or located in front

Rhode Island Not visible or located in front

South Carolina Not visible or located in front

South Dakota Not visible to driver

Tennessee Not visible to driver

Texas Not visible to driver

Utah Not visible to driver

Vermont Not visible to driver

Virginia Not visible or located in front

Washington Not visible or located in front

West Virginia Not visible or located in front

Wisconsin Not visible or located in front

Wyoming Not visible to driver

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Multi-Zone / Multi-Source Audio/VideoEntertainment Systems In a mobile video installation using multiple video source components andmultiple screens, you must manage the sources and screens in a practicalfashion. This is the intent of any well-planned multi-zone, multi-sourceaudio/video installation. The occupants should have intuitive access to what-ever source they choose to view on the screen in their zone. This requiresthat the source inputs and video screens each connect into a common, central management device so that each screen can view any of the connectedvideo sources. This device may be an external multi-zone, multi-sourceswitcher or may be a built-in part of a multimedia source unit controller.

HOW MANY SOURCES ARE POSSIBLE OR PRACTICAL?The majority of multi-source systems have two or three sources, most com-monly a DVD and VHS player. Since many consumers still own movies onboth formats, this is a practical set-up. A popular addition is also a videogaming console.

The number of possible sources is limited only by the imagination of theinstaller and the wishes-and budget-of the customer. VHF/UHF TV tuners,digital satellite (DSS/DBS) tuners, video gaming consoles, DVD-Video play-ers, VHS players, navigation systems and rear view cameras can all be con-nected into a multiple video source installation. Most mainstream videoinstallations have just two or three of these devices connected into thewhole system. Navigation or rear view cameras, for example, may only have an input to just one screen for view by the driver. Each installation will be unique in this regard, based upon the video sources in the systemsand the number of screens installed.

HOW DO THE SOURCE AND SCREEN SELECTIONS WORK?In true multi-zone, multi-source mobile A/V installations, there are reallyjust two solutions that offer the source selection and A/V output capabilities.

Dual Zone Multimedia Headunits - Where headunits incorporate multi-media capabilities, there are often provisions to control several audioand video inputs and to route those separately to two distinct zones inthe vehicle. This explains the term “dual zone.” The maximum numberof zones in a system such as this is two. Typically one zone is the mainaudio system (connected to the system amplifiers and speakers) and asecond zone is for rear seat entertainment with an audio output that willnormally connect to an IR or RF headphone transmitter. This allows theswitching and source/screen selection to take place in one convenientlocation without adding cost or installation complexity to the A/V sys-tem.

External Multi-Zone A/V Switchers - With external control of multiplesources and outputs for both audio and video into multiple zones, thepossibilities for additional sources and screens are only limited by the

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capabilities of the switching device. Typically these external switchingdevices feature three or four source inputs. Some may even contain anintegrated TV tuner.

As far as outputs, each zone is segmented to a station. Each station in thevehicle has an output for video, 2-channel audio and a controller. The con-troller is generally a proprietary keypad that allows the user to select each of the input sources one at a time. Some control keypads also allow for independent volume control and track or disc selection, where applicable.These feature-laden multi-zone, multi-source controllers may offer the mostrobust integration when used with other sources and screens in the samebrand family. The number of stations varies by switching device, but two tofour stations are common and will suit most multi-source installations.

Many IR and RF wireless headphone transmitters also feature multiple audioinputs and allow the listener to select his or her preference of audio broad-cast. Multi-source headphones offer two to four input sources depending on the brand and model.

Troubleshooting Common Video System Installation ProblemsA number of common problems arise in video systems installations.Primarily problems relate to audio and video noise, video signal strength,audio level matching between multiple sources, and mounting challenges for various source components and screens. Since most video devices operateon low current, heat is not a major concern for the components; however,direct sunlight on a video screen affects picture visibility, so install screens in locations where that will not happen.

Symptom: Noise on the video screen(s).

Solution: Check the cable(s) connecting the output to the screen input(s)

Be sure the cables are 75-ohm video cables.

Substitute the cable path with a different 75-ohm cable to establish ifthe cause of the noise is related to the placement of the original cable.

Establish if the noise is common to all screens or only one screen. Ifonly on one screen, the cable path may be the problem. If on all screens,the source component may be mounted in a noisy location or lack ade-quate shielding and isolation from external interference.

Symptom: Noise on the audio system ONLY from the video source.

Solution: Check the cable(s) connecting the audio output to the preampinputs or switching device.

Substitute the cable path with a different audio cable to establish ifthe cause of the noise is related to the placement of the original cable.

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If the noise is ONLY present when the offending source component isselected, the source component may be mounted in a noisy location orlack adequate power supply isolation from the audio circuitry. Isolationtransformers (ground loop isolators) or a power supply noise filter maybe necessary.

Symptom: Audible whining noise on the wireless headphones.

Solution: Check the cable(s) connecting the audio output to the preampinputs of the wireless headphone transmitter.


If the noise is ONLY present in the headphones (but not in the rest ofthe audio system), the headphone transmitter may lack adequate powersupply isolation from the audio circuitry. Isolation transformers (groundloop isolators) or a power supply noise filter may be necessary.

If it is a multi-source headphone system and the noise only occurs onone of the source selections, the noise is likely the fault of the sourcecomponent or audio cable, not the headphone transmitter.

Symptom: Audible whining noise on the FM modulated broadcast.

Solution: Check the cable(s) connecting the audio output to the preampinputs of the FM modulator as well as the location of the FM modulatoritself.


If the noise is ONLY present in the FM modulated broadcast (but notin the normal FM reception), the FM modulator may lack adequatepower supply isolation from the audio circuitry. Isolation transformers(ground loop isolators) or a power supply noise filter may be necessary.

Symptom: Video images are faint and colors are bleeding.

Solution: Unplug all screens connected to the video output and begin withone screen at a time.

If the colors and picture improve with only one screen and progres-sively deteriorate as you add screens, the video output will need at leasta passive splitter, possibly an active signal amplifier.

If the colors and picture are equally as bad with only one screen, sub-stitute the cable path with a different audio cable to establish if thecause of the noise is related to the placement of the original cable.

If the picture quality remains poor on all screens, the source compo-nent may be mounted in a noisy location or lack adequate shielding andisolation from external interference to the video signal.

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Symptom: Video screen image is only black and white or has abnormal scanlines present.

Solution: Check that the video source component and screens are both thesame video signal format (NTSC to NTSC, PAL to PAL, etc.).

Substitute the source component to a known good NTSC videosource using 75-ohm cable and see if the problem changes. If so, the screen may not be NTSC-compatible or may need to be manually configured to accept NTSC broadcast.

If the source component continues to have problems on a substitutedscreen, it may need configuration to NTSC broadcast format (or, if out-side the U.S., whatever broadcast format is suitable for the region).

Although S-Video is uncommon for mobile applications, black andwhite picture may also indicate a bad S-Video cable. Substitute cable fora known good cable to verify.

Symptom: VHF/UHF TV reception is poor.

Solution: Check the type and position of the antenna.

Any TV tuner application SHOULD be using a dual or quad diversityantenna for the best results.

Try alternate locations of the antenna(s) before mounting permanently.

Sometimes TV reception is simply mediocre at best in a mobile appli-cation. Areas with other wireless transmitters and urban locations withmany obstacles typically have the least pleasing TV reception in a vehi-cle. Mountainous and remote areas are also a challenge because of limit-ed channel variety and signal strength.

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SAMPLE TEST QUESTIONS

1. What colors listed are designated as the Right Rear Speaker in the EIAwire color codes?

a) Purple and Purple w/ Black Stripe.

b) Green and Green w/ Black Stripe.

c) Gray and Gray w/ Black Stripe.

d) White and White w/ Black Stripe.

2. How much power does an amplifier that measures 20 volts per channelinto 4-Ohms produce?

a) 5 Watts per channel.

b) 24 Watts per channel.

c) 80 Watts per channel.

d) 100 Watts per channel.

3. An 18dB/Octave crossover is also called which of the following?

a) 1st Order Filter.

b) 2nd Order Filter.

c) 3rd Order Filter.

d) 4th Order Filter.

4. What are the parameters that characterize a sound wave?

a) Amplitude, wavelength, intensity, speed.

b) Wavelength, frequency, speed, intensity.

c) Amplitude, wavelength, frequency, period.

d) Amplitude, wavelength, frequency, intensity.

5. Impedance is a measurement of a speaker’s voice coil resistance whilethe speaker is not in motion.

a) True.

b) False.

6. Where are active crossovers found in the audio signal path?

a) After the source unit, before the graphic equalizer.

b) After the source unit, before the amplifier.

c) After the amplifier, before the speaker.

d) Physically attached to the front of the speaker diaphragm.

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7. What does the yellow colored RCA output jack on a mobile DVD-Audioplayer do?

a) Composite Video Output.

b) Left Channel Audio Output.

c) Right Channel Audio Output.

d) Digital Audio Output.

8. Which of the following accurately describes the term “transfer function”?

a) The unique effect a vehicle has on a subwoofer’s frequency response.

b) Electronically changing the polarity of the speaker by implementing the 0-180 degree “phase” control on the headunit or amplifier.

c) Manually changing the polarity of a speaker by switching the wires at the speaker terminal.

d) An OEM interface device emulating a serial data communication protocol.

9. When a vented subwoofer enclosure is reduced in internal volume andthe vent size remains the same, what happens to the tuned frequency?

a) It stays the same.

b) It increases.

c) It decreases.

10. A 3 dB reduction in power represents which of the following?

a) 10% of the original power.

b) 25% of the original power.

c) 50% of the original power.

d) 75% of the original power.

Answers

1) A, 2) D, 3) C, 4) C, 5) B, 6) B, 7) A, 8) A, 9) B, 10) C

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Documents

Excerpt - Advanced Installer Study Guide