Copyright 2012 Compass Audiovisual, LLC Church Sound Technician Training by David S. Logsted PMP, CTS Compass AudioVisual, LLC [email protected] (505)

Copyright 2012 Compass Audiovisual, LLC

Church Sound Technician Training

by

David S. LogstedPMP, CTSCompass AudioVisual, [email protected](505) 238-2358

“there is no such thing as the perfect sound... your job is to find the closest possible approximation”

-- author unkown

(analog mixing board)


What is a sound system?an old example…

an everyday example…

Jesus teaches from a boat on the water [Luke 5:3]There was:

sound source (his voice)amplification (the water)receptors (ears of the listeners)

Cupping your hands over your mouth to be heardThere is:

sound source (your voice)amplification (the hands)receptors (ears of the listener)


What is a sound system?

Answer: An extension of someone’s speech or message

In a church sound system, ideally, the message should be replicated as transparently as possible, not coloring the sound [the message] in any way.A sound tech’s job is the most successful when he/she goes unnoticed… unnoticed because the sound is natural, everyone can hear the message clearly (what happens when something goes wrong with the sound, everyone turns around and looks at the sound tech)The sound ministry is extremely important! It enables passage of God’s word to people. Even if something as small as buzzing in the sound distracts people, the message is hindered, and lives are effected.


Topics:Sound• Waves• Acoustic & Electric Measurement

• DecayStepping Through the Mixing Board• Signal Flow!!!ConnectorsSignal TypesMicrophones• Types• UseHooking Up Multiple SpeakersCompressorsGraphic EqualizersPower Up/Power Down ProceduresHuman FactorsDemonstrationsHands On


Physical Characteristics: sound is a wave in airDefinitions: Wavelength = Velocity = v (speed of sound in air=1130ft/s)Frequency = f Period = T

Amplitude

Time

Time

1 cycle

Period (T)

Wavelength()

Time:

Distance:

Hz:

Therefore = vT

Example: For f = 20Hz , T=1/20 sec

= v / f = 1130ft/s = 56.5ft 20cps

In words:The wavelength of a 20Hzsine wave is 56.5ft

Application:1) Low f ‘s have lots of energy2) Low f ‘s resonate in a room3) 2 Sub cabinets can interact to create dead spots in the room (2 sources within 1 interfere)

Equations: = v / f T=1/f

The Nature of Sound

Waves


Physical Characteristics: Sound is comprised of multiple sine waves which add mathematically to create a sound of unique character

Example: 1kHz + 2kHz + 4kHz = 3rd order waveform

Terms: Fundamental = lowest frequencyHarmonics = higher-frequency additives which provide the characteristic sound of the source (e.g. trumpet & flute both playing an “A” note don’t sound the same)

1st Harmonic 2nd HarmonicFundamental

+ +

“Superposition”

Resultant waveform

Waves -- continued

The Nature of Sound


The Decibel: a unit of sound intensityDecibel is unit of measurement which is logarithmic. It represents a very large range by compressing the scale to a smaller range. The result is a number proportional to the original:

B=log10A

10B=A

Original #

base

log

1 = 100 = 0 10 = 101 = 1 100 = 102 = 2 1,000 = 103 = 3 10,000 = 104 = 4100,000 = 105 = 5

Did you know? The sense of hearing is a logarithmic response; so is vision. The human ear response to a tremendous range of sound energy (1 to 1trillion) – hence we need the decibel.

Logarithms

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5 6 7 8 9 10

dB

Nu

mb

er

Number

dB

Number dB1 0.002 0.303 0.484 0.605 0.706 0.787 0.858 0.909 0.95

10 1.00100 2.00

1000 3.0010000 4.00

100000 5.00

log

log

How are logarithms used to measure sound?

The Nature of Sound


How is sound intensity measured?

Doubling the intensity:

Intensity of sound wave (W/m2)

Reference value = threshold of hearingdB Level

Relative dB:

Notice: dB is a Pressure measurementexpressed in W/m2

Note: Area of sphere=4r2

Doubling the intensity, is only a 3dB increase in level!

How is sound intensity measured?

Doubling the loudness (subjective volume) = 6-10dB increase in level!

The Nature of Sound


The Decibel & Distance

change in dBr0 = 1st position

r1 = 2nd position

That is, measure dB at r0, then move to r1 & measure again.

Aside:Feedback will occur when the sound signal returning to the microphone from the loudspeaker is as strong as the original signal

How does intensity/volume change with distance from the speaker?

Doubling the distance gives a 6dB drop in intensity (~1/2 volume)

Calculate the intensity difference:10 log10(I/I0)

10 log10(r02/r2)

If r1=1m and r2=2m

10 log10(1/4) = -6 dB

The Nature of Sound


The Decibel & Electricity

The decibel is also used for electrical signals, expressed in dBVVolts

In audio, electrical signals vary from 1mV (1/1000 volt) to 1000V

-20dBV-40dBV 0dBV 20dBV 40dBV

10mV 100mV 1V 10V 100V1mV

-60dBV

Microphone Consumer Line Loudspeaker LoudspeakerDistribution

Lets take a look at the mixing console

The Nature of Sound


The Mixing Console

They’re all similar Allen & Heath GL2200

Soundcraft Spirit Live 4-2

Input Section

ChannelMic/LinePreampPhantomPhaseEQAuxiliary SendsPan & AssignMute or OnInput Fader


The Mixing Console



ChannelInput Section

Output Section

Sub Groups

Signal

Signal

Main/Stereo Out

Pan & Assign

Output Section

Pan & Assign


The Mixing Console



ChannelSignal

Signal

Pan & Assign

Input Section

Output Section

Monitor Section

Group SoloAux Solo

Channel Solo (Post/AFL)

Channel Solo (Pre/PFL)


The Mixing Console



ChannelInput Section

Return Section

Signal

Signal

Output Section

Pan & Assign

Return Section

Outboard Gear(e.g. reverb)

Dry Signal

Wet Signal

Fader

Master Section

Master Section

Lets follow the signal through the board.


The Channel Strip

Input Channel 1

Lets follow the signal flow through the board, starting with the input channel strip…


Preamplification

The Channel Strip

Phantom Power

Phase Reverse

Mic Preamp

Line Gain

Mic/Line Switch

Provides 48V DC on mic lines to power the capacitor in capacitive mics

Can be used to compensate for destructive interference (e.g. miking a drum kit)

Reverses the phase of the incoming signal by 180 degrees

Raises signal from mic level (-60dB) to line level (0db)

Raises signal from consumer line level (-20dB) to pro line level (0db)

Selects between Mic input (XLR) and line input (e.g. 1/4in, RCA)


Terms: Gain = volume, amplitudeFrequency = frequency to adjustQ = bandwidth of adjustment

gain

frequency

orgain

frequency

Two types of parametric EQ controls

Channel EQHigh-Pass Filter @ 100Hz

High-Frequency gain @ 12kHz

Mid-Frequency-1 Select Pot

Mid-Frequency-1 Gain

Mid-Frequency-2 Pots (same pots as MF1)

Low-Frequency gain @ 60Hz

EQ In/Out (pushed=In, Up=Out)Note: In means “in the signal flow/path”; Out means “out of signal flow/path” (i.e. not affecting the signal)

The Channel Strip

Parametric Equalization


Two types of parametric EQ controls

Definition: An equalization method which allows for the amplitude adjustment of a specific frequency. In fact, a range of frequencies surrounding the selected frequency are also adjusted. Therefore, the bandwidth of the frequency (Q) range is also adjustable on better boards.

Terms: Gain = volume, amplitudeFrequency = frequency to adjustQ = bandwidth of adjustment

Gain

Frequencyf1

f2Gain

Frequencyf3

f4

medium cut (- gain), medium Q

high cut (- gain), medium Q

low cut (- gain), medium Q

med boost (+ gain), med Q

low boost (+ gain), med Q

high boost (+ gain), med Q

gain

frequency

orgain

frequency

high Q

medium Q

low Q

low Q, Cut

high Q, Cut

Parametric EQ Examples

The Channel Strip


The Channel Strip

Auxiliary Sends

Aux 1-4 Pre/Post selection

Aux 5-6 Pre/Post selection

Aux Sends 1-4

Aux Sends 5-6

An Auxiliary Send takes a sample of the channel signal and sends it to a summing amp at the Aux Send Master.

Sum

Ch 1, Aux 1 Send

Ch 2, Aux 1 Send

Ch 24, Aux 1 Send

Aux 1 Master

The Aux Master controls the volume of the mix sent out the 1/4in connector.

Note: A good use for the Aux sends is for stage monitors (e.g. Aux1 for mon1; Aux2 for mon2)

Ch1 Signal Flow

EQ

fader

Insert

Aux Pre

Aux Post


The Channel Strip

Input Fader

Channel Fader

OdB = best S/N ratio

Pre-Fader Listen (PFL)

Assign Buttons

Mute

Pan Knob

Channel Identifier

Input LED

A linear volume control for mixing

Assigns channel to a pair of group faders

A “balance” control for the assigned group faders

Groups

Mutes the entire channel strip, including Aux Sends, inserts, & assigns.

Reflects input signal level at the preamp trim (top of channel)

Solo button to listen to channel (pre-fader)

Its best to run signals around 0dB

Lets talk about the next stop in the signal flow: The Groups


The Groups/Subs


The Groups/Subs

Grouping of like signals

By assigning and panning the input channels, they can be grouped together in the “groups”

Example M-Vox F-Vox Instr Pastor

Then, the groups are panned & assigned to the stereo LR output.

Pan

Assign

Aside:Notice the AFL. You can listen to each group “after the fader”


The Master Section


The Master Section

Aux Send Masters

Main LR Faders

Tones & Talkback

Monitor LEDs


The Master Section

Aux Masters

The Aux Master controls the output volume of the sum of all input channel auxiliaries.

e.g. Aux Master 1 controls the Aux Send volume for the sum of all Input Channel Aux 1 sends

Sum

Ch 1, Aux 1 Send

Ch 2, Aux 1 Send

Ch 24, Aux 1 Send

Aux 1 Master

Notice: Each Aux Master may be soloed AFL


Connectors

Returns (1/4in)

Aux Sends (1/4in)Channel Insert (1/4in TRS) Mic Input (XLR-F)

Balanced Outputs (XLR-M) Power Supply (DIN)


Connectors

Unbalanced Signals

In a standard unbalanced interconnection there are two conductors: a one signal conductor and a shield.


Connectors

Common connectors for unbalanced line-level signals1/4in phono(mono)

Returns, Aux Sends, outboard gear

Uses include:

RCA

Consumer-level signals/gear including cassette, CD

Uses include:

Inserts, headphones

Uses include:1/4in phono

(stereo)


Connectors

Common connectors for speaker-level signals

Speaker inputs, amplifier outputs

1/4in phono(mono) Uses include:

Neutrik Speakon

Uses include:

speaker inputs, amplifier outputs

Banana

Speaker inputs, amplifier outputs

Uses include:

Problem:-- not locked-- susceptible to breakage

Advantage:-- locks in place-- less susceptible to breakage


ConnectorsBalanced Signals

In a standard balanced interconnection there are three conductors: two signal conductors and a shield.

Phase=180deg

Phase=0deg

Advantage:A balanced circuit rejects noise introduced into the signal (e.g. from AC power, RFI, etc.)


Connectors

Common connectors for balanced signals

Microphones & cords, snake, outboard gear

Uses include:XLR

channel inputs, outboard gear

Uses include:

1/4in TRS phono


Example System Diagram

Mic 1-8Mon 1&2

Mic 9-16Mon 1&2

Mic 17-24Mon 1&2

Aux Send 5 Aux Send 6Channel mic Inputs

Multipin connector

Main Out RMain Out L

Processor

Cluster Amp

Sub Amp

Sub

Cluster L

Cluster R

Aux Send 3

Balance Amp

Monitor Amp

Nursery/foyer Amp

Main Insert

Graphic EQ

Channel line Inputs

Computer

Cassette

CD

Compressor

Channel Insert

Foyer R

Foyer L

Nurs 1

Nurs 2

M1

M1

M2

M2

Warning:Potentially confusingDiagram aheadPleaseWatch

carefully

Mixer

Stage

This diagram represents the connections and signal flowthrough a typical audio system


System Components

Microphones: Transducers of energy

(Instruments)(vocals)

Shure SM57Shure SM58

DynamicVery durableHigh SPL able (e.g. kick)No power required

Magnet

+ Output_

How it works…

Pos Output

Electrical energyAcoustic energy (pressure)

Magnet

+_

Neg Output


Magnet

+_


System ComponentsThe dynamic (moving coil) transducer

The microphone works by producing a small induced voltage in a coil from the effect of sound waves hitting a diaphragm.

It is very similar to a loudspeaker in reverse with a diaphragm instead of a paper cone. This type of microphone is called a moving coil microphone.

The sound waves strike the diaphragm and move it backwards and forwards at the same frequency as the sound (like the way the ear drum is moved inside the ear).

The moving diaphragm moves the coil backwards and forwardswhich induces a changing current at the same frequency as the sound. This changing current (called the signal) is sent to an amplifier which makes the changing current big enough to be used for recording or to drive loudspeakers. The loudspeaker reconverts the changing currentback into the original sound.

Dynamic MicrophoneThe loudspeaker uses a coil which can slide backwards and forwards over the central pole of a circular permanent magnet.The coil is joined by the brown bars to a paper cone, shown below.

The wire from the amplifier carries an alternating current which makes the coil (and the paper cone) move backwards and forwards at the same frequency as the changing current. The paper cone then moves the air backwards and forwardswhich creates the sound.

Dynamic Loudspeaker

Content from http://www.gcsescience.com


System Components

Microphones: Transducers of energy

capacitor

_

_

+

++++

+Batt

+

_ Pos Output


capacitor

_

_

+

++++

+Batt

+

_ Neg Output

___

_Electrical energy

Acoustic energy (pressure)

capacitor

______

+

++++

+Batt

+

_ Output

How it works…

Shure MX202(Instrument)

(ceiling, podium)Shure MX202

Condensor

(Instruments)(vocals)

Shure SM57Shure SM58

Dynamic More sensitiveReaches furtherCrisp high-end

Very durableHigh SPL able (e.g. kick)No power required

Magnet

+ Output_

How it works…

Pos Output


Magnet

+_

Neg Output


Magnet

+_


System Components

Microphone Polar Patterns

Bidirectional (figure-8)

Cardiod Super-Cardiod

Example: Shure SM58A closer look at a mic spec

Using pattern to advantage with monitors


System Considerations

Speaker Impedance

R=8

EAW SM129ZStage Monitor

Monitor Amp

R=8

R=8

R=8

R=8

R=8

…?

1R1

1R2

1Rn

+ +…

1

Calculate the Impedance:

Using: Rtotal =

Example 1: Two monitors on each output

18

18+

1Rtotal = =

28

1= 4

Example 2: Three monitors on each output

18

18+

1Rtotal = =

38

1= 2.7

18+

=83

Trend

0

Short Circuit = Blown Amp! Important Rule of Thumb: Don’t hookup more than 3 speakers/monitors in series (in line). Amps can generally handle down to 2


System ComponentsCompressors

Attack Release

Function: A compressor evens out the dynamic range (loudness) of the signal -- It brings loud sounds down.

compress

LEDs indicate compression amount, real-time -- more LEDs mean more volume reduction

LEDs indicate signal above/below threshold

Attack = how fast compression is applied

Release = how fast signal returns to normal (1:1)

Fast Attack Slow Attack

Fast Release Slow Release

Compression

Compressor Function at Threshold=4

0

24

6

8

1012

14

1 2 3 4 5 6 7 8 9 10 11 12

Input Signal

Ou

tpu

t S

ign

al

Input

Ratio = 4:1

Ratio = 3:1

Ratio = 2:1

Threshold

Threshold = when to begin reducing volume

Ratio

Ratio = how much volume reduction when over Threshold


System Components

Compressors: GatingFunction: A gate mutes the signal upon reaching the threshold – Fast attack.

Gate

LEDs indicate signal above/below thresholdRatio

Mid RatioLow Ratio

Infinite Ratio

Ratio = how much volume reduction when under ThresholdThreshold = 3

Threshold

Threshold = when to let signal pass fully/uncompressed


System Components

Graphic EQ

2531.5

Gain

Frequency (Hz)

Boost

Cut

Notice:Some overlapof frequencieseffected by each slider

4050

. . .

The graphic equalizer is typically used on the main mix to compensate for inequalitiesin a room’s frequency response. That is, certain frequencies predominate or are lacking in every room due to room resonance as well as constructive/destructive interference – the graphic EQ compensates to provide a “flat” response to the speakers.

1/3 octave EQ shown (typical): 3 sliders per octave (doubling) of frequencies


Without an automatic power sequencer, the order of system power up/down is very important to avoid pops & bumps in the speakers.

MT2400MT1200MT1200MX250

Typical Amp Rack

Power-Up Process:

1) Turn on sound board & outboard gear

2) Turn on speaker processing

3) Turn on speaker cluster amp

4) Turn on subwoofer amp

5) Turn on stage monitor amp

System Power Up/Down Example

Perform the following steps, in order, to power up (turn on) the system:

Power-Down Process:

5 ) Turn off sound board & outboard gear

4) Turn off speaker processing

3) Turn off speaker cluster amp

2) Turn off subwoofer amp

1) Turn off stage monitor amp

Here is an example system setup, showing the powering sequence

Sequence =Top-Down Sequence =Bottom-Up

Note: generally, amplifiers will be racked together with any speaker processing (e.g., crossover)

Important: Note the reverse order of steps between system Power-Up and Power-Down


Human Factors Discussion

Why are we doing this? Mixing PhilosophyInteraction with the band/peopleIntelligibility


Demonstration

Work with the compressor with a CD playingDemonstrate the Realtime Analyzer (corresponds to Graphic EQ)EQ a CDParametric EQ to fight feedback & improve intelligibilityRequests -- what would you like to see?

Ideas:


Hands-On

We’ll setup the band, the board, & the mix Work with the compressor on vocalsWork with parametric EQParametric EQ to improve intelligibilityAnswer questions

During band practice:

Documents

Copyright 2012 Compass Audiovisual, LLC Church Sound Technician Training by David S. Logsted PMP, CTS Compass AudioVisual, LLC [email protected] (505)