ECE Sound Reinforcement System Design Spring Loudspeaker Enclosure Design Project

Transcription

1 Loudspeaker Enclosure Design Project

2 TABLE OF CONTENTS Abstract i 1.0 Introduction Enclosure Design Project Summary 5 Appendix A: Activity Logs 6 Appendix B: Mechanical Drawings and Construction Details 11 Appendix C: Frequency Response and Distortion Measurements Appendix D: Wiring Diagram 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 - i -

3 1.0 Introduction My name is Rob Lingenfelter and I am a junior in Acoustical Engineering. This class is part of my required classes for my major as well as an area of interest for me. After graduation my plan is work for an acoustical consulting firm where I will directly apply the knowledge I have attained from this class. The loudspeaker enclosure project really made me appreciate loudspeakers for what they are. The first thing I learned from our enclosure design was finding the right port diameter. Our port diameter was 4 in. which looking back is way too big in my opinion. My original thought was the larger the diameter, hopefully the air is less turbulent and therefore less low end distortion. When I conducted the frequency response this did prove true; however it was mainly for lower frequencies that are harder to detect. Another thing I learned/am interested in learning more about is port positioning, and the acoustics behind the placement. I am Luke Boehnlein and I am currently a senior in Electrical Engineering on team one. I was looking forward to taking this course because I am taking a focus on audio in my electrical engineering coursework. I have been looking forward to taking ECE because I have a love for sound production, and implementing audio into my technical EE degree is an ambition of mine. From this loudspeaker enclosure design project, I learned not to belittle hands on work because it can just as easily make or break a project as theory or concepts. Also even more importantly, I learned how complex sound wave summations can get. It illustrated how helpful/necessary having a software tool is to model enclosure acoustics. Knowing the different summation zones is certainly important for applying general rules of thumb, but detailed acoustics call for a tool such as the one(s) used in this class. Out of college I want to apply the skills learned from my degree to an audio related career path. Every company and position has its own dynamics and differences in the work performed so I am still feeling around for exactly what kind of job I want to get after my last (Fall) semester at Purdue. I have also found signals in general very interesting through my time at Purdue, so that may be another possible career path. My name is Kellie Bohlig and my concentration is acoustical engineering. This coursework covers concepts that are critical within my major s concentration acoustical engineering. The class required me to apply skills learned previously from theatre, electrical and mechanical engineering courses. After interning last summer at a loudspeaker company (EV) I learned loudspeaker basics components, types, frequency response, etc as well as obtained experience testing with EASERA, but not much about the mathematics behind the enclosure design. This class provided the necessary formulas as well as in-depth information on types of speakers. I learned several things from completing the loudspeaker enclosure project the suggested procedure order (for example, cut holes last) and how to determine the size of the enclosure as well as port dimensions for a sealed-box speaker. Upon graduation I would like to apprentice for an acoustic consultant, and my ultimate career goal is to own my own acoustic consulting firm. Andrew Pawling: I am a senior in Electrical Engineering at Purdue University and I am also pursuing a minor in Theater Design and Production. I have a strong passion and interest in audio, specifically audio processing. I first took Introduction to Audio Engineering my freshman year where a very similar loudspeaker enclosure construction was completed. I was able to reinforce my - 1 -

4 loudspeaker design skills from this project. My career goal is to work in the consumer audio field doing design for audio based products or digital signal processing

5 2.0 Enclosure Design Our team decided to construct a 2-way bass reflex enclosure. We chose this classic enclosure to have an improved low end frequency response. In terms of time and construction it is also the most efficient to make. This type of enclosure has also been a tried and true design for a long too with a positive history. The components we chose for our enclosure are listed below: Dayton Audio DS " Designer Series Woofer Speaker (~$60) Goldwood GT-520 1" Soft Dome Horn Tweeter (~$12) Crossover 2-Way 2KHz 8 Ohm (~$33) We choose our two speakers because they were relatively close in sensitivity, moderately aesthetically pleasing, and fairly priced. We also chose our subwoofer because it had an EBP rating higher than 50; which is ideal for a vented enclosure. The crossover network we decided to go with was a 2 nd order 2 way crossover, with a switching frequency of 2 khz. We chose this model because it met all of our design requirements, aligned with our speakers, and was within budget. Woofer signal parameters: For our enclosure we chose to go with the SC4 alignment. This was mainly constrained to the length of the port. If the port length was not an issue we would have went with the SBB4 alignment. For our port we decided on 4in. My reasoning behind this was to avoid turbulent low end noise

6 Ajdesigner box results (Constrained and Unconstrained): (Constrained) (Unconstrained) Our final constrained box dimensions are all within a 4 in tolerance from the golden ratio proposed by ajdesigner. If the golden ratio really works then I say we re headed in the right direction. Overall our measured speaker response was fairly close to the predicted low end frequency response with the roll off starting around 30 Hz

7 Project Summary Overall the sound off competition went fairly well. It was really hard to tell whose speaker was whose but I think our speaker went in the first round. We ended up losing to the winner of the competition; however we were pretty close to the winner with regards to iclicker votes. The take away from it seems to be make your own crossover network. I think our speakers general response was pretty good compared to our competitors. I found it a bit strange that we were the only bass reflex speaker in the competition, with the rest of our competitors having some form of labyrinth speaker enclosure. Pretty much all of the speakers had times where the speakers sounded decent and other times where they didn t sound so great. The first change I would make to our design is the diameter of the port. By having such a large port I believe we boosted low end frequencies that are difficult for our ear to detect therefore not making it viable. For the future I would decrease our port diameter to the in. region. Another change would be relocating our port. As of now I don t have knowledge on port positioning but I would definitely change the location of our port from where it currently is. I would probably put the port where the drivers face. Another factor to take into account would be component selection and placement. Aside from that we were relatively happy with how our speaker performed. We obtained a relatively flat frequency response and a low distortion response

8 Appendix A: Activity Logs - 6 -

9 Activity Log for: Robert Lingenfelter Role: speaker builder/tester Activity Date Start Time End Time Time Spent Picked out speakers and crossover network 3/3/15 5:30 pm 7:00 pm 1.5 hrs Used ajdesigner.com to calculate speaker dimensions and port size Constructed entire speaker enclosure (cut holes, soldered connections, mounted speakers, installed port, glued and sanded) 3/12/15 2:00 pm 4:00 pm 2 hrs 4/11/15 12 pm 6 pm 6 hrs Edited Loudspeaker design document 4/19/15 1 pm 2pm 1 hr Conducted frequency response and distortion measurement and distortion measurements 4/26/15 8 am 9 pm 1 hr Made Spark Challenge Presentation poster 4/27/15 6pm 7pm 1 hr Finalizing loudspeaker report 5/2/15 1 pm 4pm 3 hr - 7 -

10 Activity Log for: Luke Boehnlein Role: Component selection Activity Date Start Time End Time Time Spent Picked out speakers and crossover network 3/3/15 5:30 pm 7:00 pm 1.5 hrs Used ajdesigner.com to calculate speaker dimensions and port size 3/12/15 2:00 pm 4:00 pm 2 hrs - 8 -

11 Activity Log for: Kellie Bohlig Role: component selection Activity Date Start Time End Time Time Spent Picked out speakers and crossover network 3/3/15 5:30 pm 7:00 pm 1.5 hrs Used ajdesigner.com to calculate speaker dimensions and port size 3/12/15 2:00 pm 4:00 pm 2 hrs - 9 -

12 Activity Log for: Andrew Pawling Role: component selection Activity Date Start Time End Time Time Spent Picked out speakers and crossover network 3/3/15 5:30 pm 7:00 pm 1.5 hrs Used ajdesigner.com to calculate speaker dimensions and port size 3/12/15 2:00 pm 4:00 pm 2 hrs

13 Appendix B: Mechanical Drawings and Construction Details

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15 Appendix C: Frequency Response and Distortion Measurements

16 Frequency Response Distortion Measurements The results from our speaker response measurements show a relatively flat frequency response; which is ideal. Our distortion response at 1 khz was roughly -56 db giving us a distortion response of 2% which is pretty low

17 ECE Sound Reinforcement System Design Appendix D: Wiring Diagram Spring 2015