ECE 40020 Sound Reinforcement System Design Spring 2015

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Loudspeaker Enclosure Design Project

Project Report Evaluation – Team ID: 04-Sonic Boom

Ben Capano, Bryan Marquet, Sean Obrecht, Aditya Sharma

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TABLE OF CONTENTS

Abstract 3

1.0 Introduction 4

2.0 Enclosure Design 6

3.0 Project Summary 9

Appendix A: Activity Logs 10

Appendix B: Mechanical Drawings and Construction Details 15

Appendix C: Frequency Response and Distortion Measurements

Appendix D: Wiring Diagram

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Abstract

We designed a labyrinth speaker enclosure to improve low frequency response. The enclosure

consists of two drivers, one high frequency and one bass/midrange frequency, and a crossover

network. The internal distance traveled by rear radiation waves is 6 ft long to match a quarter

wavelength of 45 Hz. This provides enough room for the rear radiation waves to be in phase with

the front radiation at low frequencies. The design was successful in producing low frequencies

with minimal distortion as low as -30dB at 25 Hz. A reasonably flat frequency response curve

was achieved between 50Hz-16kHz. A second iteration of the design could have a higher quality

crossover network with better components that can function at higher at a higher power rating.

General Specifications:

Frequency response: 50 – 16,000 KHz ± 4 dB

Power handling capacity: 60 watts

Crossover Frequency: 2500 Hz

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1.0 Introduction Ben Capano This class caught my attention as an interesting application of electrical engineering

concepts I had already learned as well as sound design concepts that I had no previous

knowledge of. I wanted to learn about how speakers work and what goes into creating quality

sound environments. Working on the loudspeaker enclosure design project has showed me that

there are many different ways to design a speaker and it all depends on what you want out of the

frequency response. I do not have any intentions of pursuing a career in sound but I would really

like to build more speaker enclosures in the future for my home as a hobby.

Bryan Marquet

As a senior in Electrical Engineering, I was interested in ECE 40020 to learn more about

speaker design before graduating. I have built a few enclosures before this class without knowing

what I was doing, and I wanted to take this class to increase my hobbyist knowledge. I learned

how to effectively design and realize a speaker enclosure by completing this design project. At

this time I do not have professional acoustics-related goals, but I enjoy building enclosures and

will continue doing so with my new skill set.

Sean Obrecht

As an acoustical engineer focusing on sound system engineering, this class is required by

my major, but even if it wasn’t required, I would have taken it anyways. I have always been

interested in audio and the way sound works, so I thought that this would be a very informative

class. I took the freshman seminar version of this class last year and thoroughly enjoyed it, but

that class was simply a brief introduction to this class, and I wanted to learn more about how

sound works within acoustic spaces, not just enclosure design. Because of this project I have

learned about the important elements of designing a vented loudspeaker and how the properties

of the drivers dictate how the enclosure is designed. After college I intend to pursue a career in

audio/ acoustics, either doing consulting work, sound reinforcement for theaters, or sound

design, so I felt that this was an essential class in helping me prepare for the professional world.

Aditya Sharma As an electrical engineering major, I didn’t get any experience in acoustics or sound

reinforcement during my course of studies here at Purdue University. I have been playing variety

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of musical instruments from a very young age. I have also been a huge fan of advancements in

acoustics world, namely home and portable audio - headphones, home theater etc. I got

interested in this class because it provided me with an opportunity to get more insight on how

sound reinforcement systems work and I was also able to receive some design experience, that is

not very common in electrical engineering track. I was able to land a job as a development

engineer for their acoustics sensor team because my employer noticed this class on my transcript

and was really impressed. I know we didn’t cover acoustic sensor designing in any form but this

class taught me fundamentals of sound, which combined with my knowledge in electrical

engineering will definitely help me succeed in future.

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2.0 Enclosure Design Our team decided to construct a labyrinth speaker because of the improved bass response

that labyrinths can offer compared to other designs. We chose to have two drivers instead of

three because of simplicity and less variables that could contribute to unwanted cancellation near

the crossover frequencies. Cost was also a factor; we only had $100 to spend on the speaker

elements and crossover, so we chose to buy two higher quality drivers instead of three lesser

quality ones.

List of components:

● Fane Sovereign Series 12 inch Prosound Woofer:

○ Usable frequency range: 45 Hz - 4 kHz

○ RMS power handling: 200W

○ Impedance: 8-ohm

○ Qts: 0.44

● Visaton DT94-8 0.8” Polycarbonate Dome Tweeter:

○ Usable frequency range: 1.2 kHz - 22 kHz

○ RMS power handling: 50W

○ Impedance: 8-ohm

○ Qts: 0.54

● Monacor 2 Way Crossover Network:

○ Crossover frequency: 2.5 kHz

○ Power handling: 60W

○ Impedance: 8-ohm

We chose these two drivers for a number of reasons. First of all, the frequency responses

of both of them needed to have enough overlap for a crossover network to be able to adequately

function. This is possible with these elements seeing as their ranges overlap from 1.2kHz to

4kHz. We chose a crossover network with a crossover frequency of 2.5kHz for our loudspeaker

enclosure because this was in the middle of the overlapping range, thus we predicted to have a

smooth frequency response in this region. Second, we wanted really solid response at low

frequencies, which is why we chose a bass range driver that was capable of outputting a lot of

power. As will be shown later, our loudspeaker was capable of producing very quality sound at

low frequencies with minimal distortion. The tweeter we selected also had low Qts and the same

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impedance as the bass driver and crossover network. Lower Qts is desired for vented enclosures,

and at this price range, this is about as low as we could get for a tweeter and bass driver. In

hindsight, it would have been more favorable to spend less of our budget on the bass driver and

instead buy a higher quality crossover network capable of handling more power.

The internal labyrinth length is 6 ft. This was determined by finding the half-wavelength

of 45Hz, which is Fs of our low-frequency driver. This allows the sound from the rear radiation

of the driver to be in phase with the front radiation sound by the time it exits the labyrinth

speaker, minimizing any undesirable combination or cancellation.

ajdesigner.com results

This shows the dimensions of the box as predicted by ajdesigner. As shown in Appendix

B, our final w x d x l dimensions are 16in x 16in x 40in, which is very close to what is modeled

here in ajdesigner. We constrained the length and depth for the labyrinth and then we used the

suggested width (or rather, height) that ajdesigner gave us.

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This output shows the predicted low frequency response curve of our loudspeaker

enclosure. Our final frequency response curve (Appendix C) is fairly close to this predicted

curve in that by 50 Hz, the response flattens out. This quality performance at low frequencies is

what we wanted out of our loudspeaker enclosure. The parameters and dimensions of the

enclosure as determined using ajdesigner are as follows:

Vb: 10016.9 in^3

Fb: 45 Hz

F3: 45.72 Hz

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3.0 Project Summary

Our speaker performed well in the “Sound Off” competition. It was the only speaker that

ever took the lead from the winning speaker at any point in the song. In Team 4’s opinion, we

believed we did indeed have the best speaker. Another comparison was between the frequency

response of our enclosure against others. Based on the data on the website, our enclosure has a

competitive, flat response across frequencies of all of the speakers built. Within the required

range of response, our speaker has a maximum difference of 15 dbSPL, which is nearly the same

as team one magnitude shift. Finally, we have very low distortion, even at incredibly low

frequencies, which is extremely encouraging. All of these factors lead us to believe we have a

strong speaker, but there is always room for improvement.

Our budget was the defining factor for quality of components, but we were still able to

find well-performing speakers given the constraint. The easiest way to improve our system

would be to either design our own crossover network or buy a new one. When we purchased our

speakers we misunderstood the budget and did not buy a crossover network. This mistake forced

us to buy an extremely cheap crossover network to stay close to the budget. The crossover

network is only rated for 60 W, which is nothing near the ratings of the speakers. If we installed

a new crossover at a higher power rating and with more robust components, the system would

like perform at a higher level. Also, we did not caulk the wood together because we did not want

to permanently seal some of the sides. These imperfections could allow unwanted sound to

escape. Filling in any gaps would likely increase the performance of the system.

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Appendix A:

Activity Logs

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Activity Log for: Ben Capano Role: Enclosure design and construction

Activity Date Start Time End Time Time Spent

Ordered drivers and crossover network

3/10 10:15am 11:15am 1

Helped create dimension drawings

3/24 10:15am 11:15am 1

Acquired wood, made markings for cuts

4/14 10:00am 11:00am 1

Drilled necessary holes in speaker

4/17 11:00am 12:00am 1

Assembled and glued inner labyrinth pieces

4/20 1:00pm 3:00pm 2

Assembled/glued outer pieces

4/21 2:00pm 4:00pm 2

Inserted stuffing material

4/22 1:00pm 2:00pm 1

Drilled drivers into front, inserted wiring

4/26 2:00pm 5:00pm 3

Closed box, completed speaker

4/28 10:00am 11:00am 1

Began distortion/frequency response testing

4/28 2:00pm 3:00pm 1

Writing Report

5/5 3:00pm 4:00pm 1

Writing Report/ajdesigner work

5/6 7:30pm 9:00pm 1.5

ajdesigner summary workds

5/7 5:30pm 6:30pm 1

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Activity Log for: Bryan Marquet Role: Hardware Engineer

Activity Date Start Time End Time Time Spent

Ordered drivers and crossover network

3/10 10:15am 11:15am 1.0

Helped create dimension drawings

3/24 10:15am 11:15am 1.0

Acquired wood, made markings for cuts

4/14 10:00am 11:00am 1.0

Drilled necessary holes in speaker

4/17 11:00am 12:00am 1.0

Assembled and glued inner labyrinth pieces

4/20 1:00pm 3:00pm 2.0

Assembled/glued outer pieces

4/21 2:00pm 4:00pm 2.0

Inserted stuffing material

4/22 1:00pm 2:00pm 1.0

Drilled drivers into front, inserted wiring

4/26 2:00pm 5:00pm 3.0

Closed box, completed speaker

4/28 10:00am 11:00am 1.0

Began distortion/frequency response testing

4/28 2:00pm 3:00pm 1.0

Established report responsibilities

5/4 1:00pm 2:00pm 1.0

Wrote Section 3.0

5/5 4:00pm 5:00pm 1.0

Created Wiring Diagram

5/7 4:00pm 5:00 1.0

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Activity Log for: Sean Obrecht Role: Enclosure Designer, Component Selection

Activity Date Start Time End Time Time Spent

Enclosure Selection

3/3/15 10:15 am 10:45 am 0.5 hr

Component Selection

3/10/15 10:15 am 11:45 am 1.5 hr

Enclosure Design/ Drawing

3/24/15 10:15 am 11:45 am 1.5 hr

Report

3/4/15 1:00 pm 1:30 pm .5hr

Total 4 hrs

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Activity Log for: Aditya Sharma Role: Enclosure Designer

Activity Date Start Time End Time Time Spent

Brainstorming and discussion - enclosure type

3/3/15 10:15 am 10:45 am 0.5 hr

Components selection

3/10/15 10:15 am 11:45 am 1.5 hr

Designing the enclosure

3/24/15 10:15 am 11:45 am 1.5 hr

Report

3/7/15 5:00 pm 6:00 pm 1hr

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Appendix B:

Mechanical Drawings and Construction Details

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These are the measurements for the wood needed to construct the loudspeaker enclosure. The final box has height 40”, width 16”, and depth 16”.

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Appendix C:

Frequency Response and Distortion Measurements

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Full range frequency response

This indicates that we do in fact have fairly flat (+5d) frequency response from 50Hz - about 15kHz. This is very good for an enclosure with two drivers. Distortion at 50 Hz

This graph shows that there is very little distortion at low frequencies. At 50Hz, distortion is about -30dB. This is the case all the way down to about 25Hz, which is due to the capabilities of our low-frequency driver.

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Appendix D:

Wiring Diagram

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Wiring Diagram: