Loudspeaker Enclosure Design Project - Purdue … 40020 Sound Reinforcement System Design Spring 2015 - 3 - 2.0 Enclosure Design Type of enclosure: Two-way labyrinth Components chosen:

ECE 40020 Sound Reinforcement System Design Spring 2015

Loudspeaker Enclosure Design Project

^Very candid “selfie” of Group 2 taken during class.


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TABLE OF CONTENTS

Abstract Your job is to design and construct a loudspeaker enclosure of a prescribed type (sealed box, bass reflex, labyrinth, damped pipe with constant cross-section, or damped pipe with tapering) and measure its performance. Compare and contrast both the expected and the measured performance of your design vs. the other enclosure types. Finally, suggest possible improvements that could be made in a “second iteration” of your design. General Specifications:

Frequency response: 50 – 16,000 KHz ± 4 dB Power handling capacity: 60 watts

Abstract i

1.0 Introduction 1

2.0 Enclosure Design 3

3.0 Project Summary 7

Appendix A: Activity Logs 8

Appendix B: Mechanical Drawings and Construction Details 13

Appendix C: Frequency Response and Distortion Measurements 19

Appendix D: Wiring Diagram 21


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1.0 Introduction Schyler Curtice I chose to take this course because I took THTR 353 (Theater Audio Technology) which allowed us to design a sound system for a theater. I was given the amphitheater in that course and used the dimensions to calculate things such as the reverberation time with and without an audience, critical distance and PAGNAG. We then got to specify what loudspeakers we would use and what coverage patterns they produced. We also chose a mixing console, microphones, digital signal processor and other electronic equipment. I enjoyed the process and it led me to take this course. I learned the many different types of loudspeaker enclosures through this design project along with how each design produces unique responses. I also learned how to construct a labyrinth which I previously had not done when constructing a loudspeaker. I hope to one day use my knowledge of theaters and equipment to be able to consult various noise transmission problems in a project-based environment. Rob St. Claire Aside from ECE 40020 being a selective option for the Acoustical Engineering plan of study, my interest in it was also sparked by THTR 353. Additionally, I took Prof. Meyer’s Intro to Audio class my freshman year where we built a loudspeaker in a similar project. This course takes projects from both of those courses and repeats them more in depth, with more theory and calculations. Loudspeaker parameters were nothing but a bunch of numbers to me as a freshman, but now I understand how certain enclosure types fit with certain driver specifications. The labyrinth design that we’re working on this semester actually took internal reflections and wavelengths into consideration, and will hopefully produce a better result than our silly sealed box from freshman year. As far as career goals are concerned, I’m very interested in room acoustics and design, which makes me very interested in the EASE software. This summer I’ll be interning for Apple on one of their audio hardware teams, so I’m planning on being pretty versatile in the audio engineering world. Schuyler Putt As a student studying acoustical engineering, I made sure to take ECE 40020. It ties much of what I have studied in the THTR and ECE departments together, and the topics covered in this course make it the apex of the acoustical degree. In this same vein, completing the loudspeaker enclosure design project has given me a tangible way to bring many of my studies together. Having taken ECE 201 and 202, I understand what makes the crossover work. Having taken several THTR classes, I appreciated the careful art that is selecting the drivers and other components. This project allowed me to do all of that with my own two hands, and that’s a valuable experience for cementing what I have learned into my mind. I’m undecided about what I would like to do as a long term career goal, but ME and EE-based acoustics are at the forefront of my interests. Last summer I worked as an EE intern for Delphi Automotive, designing circuit boards and a haptic warning system that uses seat vibrations to warn the driver of a semi-autonomous car to retake control. This summer I will work a vibrational ME internship at John Deere, effectively balancing out the EE on my resume and, I hope, giving me countless opportunities for my first real job!


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Adam Walt I was involved with and developed a passion for technical theatre in high school. I wanted to continue that passion in college. I met Joel Ebarb at a theatre festival in Illinois and he introduced me to the Acoustical Engineering program. That somewhat sealed the deal for me and I committed to Purdue not long after. One of my long-term career goals has always been to design theatres, so this class seemed like it would be very interesting and teach me a lot more about sound reinforcement. This class made me realize that I have taken speakers for granted. I used to think you just mounted some cones or tweeters in a box and that was that. I never realized all the various designs that took place on the inside, such as labyrinth designs. It really has given me a new appreciation for the work that people put into designing them.


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2.0 Enclosure Design

Type of enclosure: Two-way labyrinth

Components chosen: 1) Crossover – MCMelectronics 12 dB 3 kHz 2-way crossover (part. No

60-10565)

We chose this crossover because of the quality for the price. The

crossover frequency was ideal for what we wanted.

2) Woofer – MCMelectronics 10” 100 W RMS Carbon Fiber woofer

(part no. 55-1556)

We chose this woofer because we wanted to spend about half of

our budget on a quality low frequency woofer and this one fit our price

range. It has a very rigid, carbon fiber cone that is necessary for

labyrinth enclosure designs.

Small signal parameters:

Re: 5.6ohm

Le: 1.78mH

Fs: 38Hz

Qts: 0.39

Qes: 0.42

Qms: 6.13

Vas: 44.9 (liters)

3) Tweeter – Parts Express 1” 6 ohm Silk Dome Tweeter (part no. 264-

1386)

We chose this tweeter because we wanted the outside components

(tweeter and woofer) to be where we spent most of our money and it was

in our price range of around 30 dollars. The silk dome should provide us

with a warm sound which is what we are looking for.


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We were not able to use AJDesigner due to us not finding a labyrinth calculator. Therefore

we used the labyrinth calculator on DBDynamixAudio

(http://dbdynamixaudio.com/70/labyrinth-vent-bass-reflex-enclosure-calculator/). Below are the

calculations

LABYRINTH VENT BASS REFLEX ENCLOSURE CALCULATOR

By: DB DYNAMIX AUDIO

http://dbdynamixaudio.com/70/labyrinth-vent-bass-reflex-enclosure-calculator/

Conversions:

1 cubic feet 28.32 liters

1 inches 25.4 millimeters

120 sq. inches 774.19 sq. cm

28.32 liters 1 cubic feet

25.4 millimeters 1 inches

774.19 sq. cm 120 sq. cm

Driver Specifications:

# of Drivers: 1

FS: 38 hertz

QTS: 0.39

VAS (Cubic Feet): 1.585451977

Driver Displacement: 0.00492126 cubic feet

Enclosure Specifications:

Net Volume (Cubic Feet): 3.610819481

Port Tuning: 15.746049832 hertz

Port Area: 33 sq. inches

Slot Port Width (inches): 3 required

Recommended Tuning: 29.442403772 hertz

Recommended Alignment: 1.418065499 cubic feet

39.337359519 hertz

Maximum Dimensions:


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External Height (inches): 12 required

External Width (inches): 40 required

External Depth (inches): 24 required

Material Thickness (inches): 0.5 required

Bracing Ect. Displacement: 0 cubic feet

Panel Dimensions:

Top (Green): 40 X 24

Bottom (Green): 40 X 24

Front Baffle (Orange):

36.5 X 11

Rear Baffle (Yellow): 40 X 11

Side Panel (Blue): 23 X 11

Side Panel (Red): 23.5 X 11

Port Wall 1 (Teal): 20 X 11

Port Wall 2 (Purple): 32.5 X 11

Port Wall 3 (Pink): 32.5 X 11

***See Appendix for color-coordinated diagrams

The golden rule is .62: 1: 1.62 which goes to 1: 1.61: 2.61

Our ratio is 12: 24: 40 which goes to 1: 2: 3.33 and is not exactly the golden ratio, but

does have a very close relation to the ratio.

Calculated loudspeaker parameters:

VB (box volume) = 3.61 cubic feet

FB (box resonance) = Fs*sqrt((VAS/VB)+1) = 45.6 Hz

F3 (-3 dB half power frequency) = 14.72

LP (length of port) = 3.5 inches


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Frequency Response:

The woofer should have a frequency response between 38 to 4000 Hz. The recommended

alignment frequency is about 39 Hz, which is close to the minimum frequency, but the max does

not quite reach on this graph to what it should be (4000 Hz). This only considers the woofer’s

specifications, and not the low end reinforcement that will come from the enclosure design. See

Appendix for actual measured frequency response of the entire loudspeaker system.


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3.0 Project Summary

The music sample used in the sound off competition made a couple things about our

speaker response fairly clear. Most notable was the peak on the frequency response curve at 3

kHz that made the high end sound “sharp” or abrasive. This could’ve been simply a factor of the

tweeter’s construction or a function of the crossover point at 3 kHz. Our enclosure did a stellar

job of reinforcing the bass response, enabling the frequency response to reach down to around 25

Hz. The woofer produced clear, tight low end, which sounded very good to human ears.

The thing that made the winning group’s speaker sound so good had to have been their

customized crossover network and crossover point of 2.75 kHz. Their woofer was of lower

quality than ours and their enclosure did less to help the bass response, plus their titanium dome

tweeter typically produced lower quality sound in the freshman classes. However, their

loudspeaker produced remarkably full, balanced, and smooth sound that was unrivaled by any of

the other loudspeakers. It produced tight, clear low end and smooth trebles with no unfriendly

peaks or valleys in what surely was an extremely smooth frequency response curve. That must

have been a function of their customized crossover network.

I’d be interested to see what effect a custom-tuned crossover network would have with

our speaker components and our enclosure design. I predict it would help smooth out that

tweeter peak at 3 kHz and improve overall balance and clarity.

Also, when I designed the enclosure, the calculator I used only generated box dimensions

under a preset design. It used a couple parameters of the woofer, but I question its legitimacy in

hindsight because it never told me anything about frequencies. That’s what I get for using a

random online calculator, and while it did end up working out pretty well, the design had a lot

more potential with more rigorous calculations or better software.

This summer I’ll be working for Apple’s audio hardware team, where I surely will learn a

lot more about how to optimize loudspeaker performance with limited space. It would be

interesting to redo the design and construction of this project with that knowledge, and ample

time to fully customize an enclosure, fine-tune a custom crossover network, and run more

performance tests.

- Rob St. Claire


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Appendix A:

Activity Logs


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Activity Log for: Schyler Curtice Role: EASE Designer/Documenter

Activity Date Start TimeEnd Time

Time Spent

Looked up loudspeaker components 3/11/2015 5:30 pm 6:30 pm 1 hour Helped begin work on loudspeaker, began reports for loudspeaker

4/14 6 pm 8 pm 2 hours

Worked on loudspeaker 4/15 6:30 pm 7 pm ½ hour Worked on loudspeaker report

4/27 3 pm 4 pm 1 hour

Helped finish loudspeaker

4/28 10:30 11 am ½ hour

Worked on loudspeaker report

4/29 2 pm 3 pm 1 hour

Total:

6 hours


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Activity Log for: Rob St. Claire Role: Loudspeaker Designer/Constructor

Activity Date Start Time End Time Time Spent

Looked up loudspeaker components 3/11/15 5:30 pm 6:30 pm 1 hour Designed loudspeaker enclosure


Began construction on loudspeaker


Continued construction on loudspeaker

4/15 10:30 am 11:30 am 1 hour



Finished loudspeaker construction, ran initial response tests

4/27 10:30 am 12 pm 1.5 hours

Secured front face, sound tested with various musical samples

4/28 10:30 am 11 am .5 hours

Finished loudspeaker report, moved loudspeaker to classroom

4/29 2 pm 3 pm 1 hour

Created loudspeaker project poster


Total:

18 hours


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Activity Log for: Schuyler Putt Role: EASE/Loudspeaker Designer


Time Spent

Looked up loudspeaker components 3/11/2015 5:30 pm 6:30 pm 1 hour Helped construct loudspeaker

4/14 7 pm 8 pm 1 hour

Worked on loudspeaker 4/24 3 pm 5 pm 2 hours Ran initial response tests on loudspeaker

4/27 10:30 am 12 pm 1.5 hours

Total:

5.5 hours


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Activity Log for: Adam Walt Role: Designer


Time Spent

Looked up loudspeaker components 3/11/2015 5:30 pm 6:30 pm 1 hour Soldered loudspeaker wires

4/24 5:30 pm 7:30 pm 2 hours

Secured front face, sound tested with various musical samples

4/28 10:30 am 11 am .5 hours

Moved loudspeaker to classroom

4/29 2 pm 3 pm 1 hour

Total:

4.5 hours


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Appendix B:

Mechanical Drawings and Construction Details


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Figure 1 (Above): This front view of our loudspeaker shows it lying on its side. It is color coded to match the pieces on page 15.

Figure 3 (Above): A tilted side view (open box)

Figure 2 (Below): Side view of speaker (open box)


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Figure 4 (Left): These pieces are each individual wooden component to our loudspeaker. They are color coded to match figures 1-3


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Construction Details: We began by taking the outer wooden components and gluing them together, using wood glue and clamps for security. The machine shop was not able to cut our 9” woofer hole initially, but once we obtained the necessary tools we cut holes for the drivers and connector, glued the front piece, finished enclosure assembly and began electronic installation (see schematic diagram in Appendix). We soldered six wires to the crossover network, then glued a backing piece of wood to the inside of the enclosure and screwed the crossover network to it. We then attached the drivers to the front face with screws and soldered their respective wires to them. Lastly, we soldered the connector to its wires. The connector was screwed into the side panel, which was not yet secured to the enclosure (seen removed from picture above). We lined the labyrinth with acoustic absorbent material, then ran our initial sound tests without the side panel securely fastened. We tried reversing the polarity of the tweeter, then undid it, and finally secured the side panel.


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Appendix C:

Frequency Response and Distortion Measurements


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Note the very smooth response from 1 kHz down, and the significant bump at 3 kHz. The high end tails off at about 20 kHz, well above the project guideline of 16 kHz. When running pure sine waves at selected frequencies through the loudspeaker, the lowest frequency that produced sound was 22 Hz.


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Appendix D:

Wiring Diagram


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Documents

Loudspeaker Enclosure Design Project - Purdue … 40020 Sound Reinforcement System Design Spring 2015 - 3 - 2.0 Enclosure Design Type of enclosure: Two-way labyrinth Components chosen: