Loudspeaker Design Project
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Loudspeaker Design Project Kyle Persohn Fall 2007 Transducer Theory Michigan Technological University Loudspeaker Design Project – Kyle Persohn Table of Contents Datasheet Design Statement Initial Design Revised Design Final Design Cabinet Design Crossover Design Accounting Drafting Construction As-Built Plans Initial Listening Evaluations Testing and Tuning Final Listening Evaluations Final Report Gallery ThankYou I owevery big thanks to MadisoundSpeaker Components for providingdrivers and crossover parts at educationalrates to makethis projectpossible on a strictbudget. In particular,thank to AdamJohnson who took time out of hisafternoon to helpinspire this final design. I highlyrecommend Madisound to anyspeaker builder looking for an onlineretailer who providesa vastproduct range, competitive pricing,and excellent customer support. ?r' fu-nunaot tladlsound Foi/rr(-totd.€fu,n Scan-spek - LPG Speaker Peerless-Seas-Keiga Gomponents,lnc. HhVi-Audax-Hovland Founhk - Accubn Distributorof Loudspeakers& ComponentsWorldwide Mr. Adam Johnson P.O,Box 1l28g Tcl:008{11-3433 Mafion, YU537ll4 USA F.x:C0E-E31€771 www.firdaound.oofvl *mQmeOlound.cofn WinSpeakerz Modeled Plots 450 Watts Input Power Frequency Response Impedence Linear Excursion Features Specifications • High SPL ouput Dimensions 12.50” X 61.00” X 13.00” • Deep low-frequency extension W X H X D • Affordable user replaceable Connectors NL-4 Speakon voice coil on tweeters • Horn-loaded directivity Frequency Response 38 Hz – 19.5 KHz (est.) • Dome tweeter clarity Max SPL Output 119 dB (modeled) • Even frequency response • Robust finish Power Handling Up to 450 Watts (est.) • Excellent mechanical grounding • Solid construction Woofers Peerless 10” 830668 Tweeter Morel MDT37 Copyright © 2007 Kyle Persohn, All rights reserved. Other brand names are trademarks or registered trademarks of their respective owners. Transducer Theory [FA4740] Fall 2007 These HiFi PA speakers are designed for use in the Ensemble Room (209) in the Michigan Tech Rozsa Center. This acoustical system provides a unique balance between volume capability and audio quality bringing you hard hitting bass and elegant treble at impressive volume levels. Featured in this system are two Peerless 830668 10” Woofers and a Morel MDT37 per cabinet arranged in a “woofer-tweeter-woofer” configuration. The WTW arrangement allows the high and low frequencies to blend on the listening plane (tweeter height). The listening plane is conveniently located at ear level when sitting at the computer workstation in Room 209. The use of two woofers utilizes the combined audio power of two lower sensitivity but higher quality drivers to blast low frequency extension at high volumes. The mini horn-loaded MDT37 boasts the directivity and high SPL of a compression driver while still maintaining the smoothness and lower distortion characteristics of a dome tweeter. A passive 4th order Linkwitz-Riley crossover network provides the frequency separation between the high frequency tweeter and the low frequency woofers. The L-R design is favorable over the traditional Butterworth design because there is a flat 0db response at the 2 KHz crossover point instead of the normal 3db peak. This 4th order vented box in constructed primarily of MDF with A/C plywood reinforced baffles and cross-bracing. The dual baffle design keeps cabinet resonance to a minimum because the varying density materials discourage standing waves. Internal dampening features Black Hole acoustic foam to reduce unwanted reflections. The 2” ABS port is located well below listening plane where airflow will not disturb performance. A coating of black truck bed liner gives the outside finish a robust look and feel. Adjustable floor spikes provide cabinet balancing and additional mechanical grounding on carpeted surfaces resulting in tight, punchy bass. Sign up for swipe access in the VPA office to try them for yourself! Professional Sound High Fidelity PA Speaker Designed & Built By: Kyle Persohn Transducer Theory Loudspeaker Design Statement Kyle Persohn FA4740 Christopher Plummer Michigan Technological University Design Statement Persohn Introduction The speakers to be built are being designed for the Visual and Performing Arts Department of Michigan Technological University. They are intended for use in the Hagen Practice (Rozsa 209) also known as the Ensemble Room. The design will borrow concepts from PA speakers in efforts to achieve high volumes, however a higher emphasis will be put in fidelity and bass response than one would find in a traditional PA cabinet. The completed set is expected to meet these requirements: • Reasonably sized, but well mechanically grounded • Directed coverage • Bass response below 60Hz • High sensitivity/SPL at least 93dB • Driver selections and crossover design that keep audible breakup modes to a minimum • Robustness for a college environment • Strict budget of $600 Budgeting I started my driver hunt with budget as the primary limiting factor. Using the general guideline of 40% drivers, 35% crossover, 25% cabinet, I allocated a reasonable amount of resources and used that to limit the overwhelming choices of drivers. Preliminary searches yielded some promising options from Selenium, Eminence, Peerless, and B&C. I originally disregarding Peerless for not having enough sensitivity and the Seleniums were negated for their questionable quality. After examining a few specification sheets, I came to the quick realization there is a heavy tradeoff between cost, sensitivity, and bass response (and enclosure size; however, I decided I could be the most flexible with this variable). It is extremely difficult to find economically priced drivers that have a pro-sound level SPL output without sacrificing low end response. Drivers Originally, I was open to 2-way and 3-way designs. With hopes of having better bass response I looked briefly into 3-way designs. With the additional driver and doubling of crossover parts these systems met the physical specification requirements the best; however they didn’t quite make the Page 2 of 9 Design Statement Persohn budget cutoff. I then focused mainly on 2-way designs primarily for budgetary reasons with hopes of maximizing whatever bass response I could get out of them. My first potential system had an Eminence Alpha-8A woofer paired with a B&C DE-10 compression tweeter. I came across the Eminence drivers on cost based searches and I sought out the B&C tweeters from a review on the Loudspeaker Designer’s Selection Guide. In contrast to the suspiciously smoothed looking frequency response graphs of the Selenium drivers, the B&C plots resembled measurements taken by a third party (Stout, 2007). This system had high sensitivity while still making the budgetary cutoff. Unfortunately when following the manufactures recommended tweeter crossover point, much of the driver top end break up would be audible. I chose to replace the B&C with an Eminence PSD2002 which features a 2” voice coil allowing it to crossover slightly lower and eliminating more of the woofer’s breakup. Upon modeling this design in WinSpeakerz I was disappointed to discover the design was only going to get a response down to 80Hz at -3dB (See Figure 1). Figure 1: Eminence Alpha-8A Page 3 of 9 Design Statement Persohn Woofer Selection A reasonable compromise is to add a second driver to a 2-way system. Having a second driver expands the possibilities to woofers that might not necessarily have a high enough sensitive by themselves. By combining two high fidelity drivers their combined SPL output can reach that of pro- sound drivers. This opened up a realm of drivers I had discounted before due to their inadequate sensitivity. The Peerless SLS 830668 10” woofer, for example, has an SPL of 88.7dB, but combined with a second can approach 95dB. This particular driver also has a suitable response down to 38 Hz which is considerably better than the previously mentioned 2-way design (See Figure 2). This compromise adds some additional expense to the traditional 2-way design by adding an extra driver; nonetheless, with half of the crossover parts necessary as a 3-way design this revised 2-way has bass response at a reasonable cost (Electus, 2001). Although a bit on the pricey side, dual woofers in a 2-way configuration seem to be the best balance between SPL, bass response, and cost-effectiveness. Figure 2: Peerless 830668 Page 4 of 9 Design Statement Persohn Tweeter Selection With the initial 2-way design it seemed necessary to use a compression driver as a tweeter to get the high sensitivity required by the system. I looked at many compression drivers that were easily horn- loadable to obtain some directivity and additional SPL. In my readings, I discovered some of the negative effects that keep horn-loaded designs out of most studios and are limited to PA systems where quality isn’t so much of an issue (Newell, 2007). A horn provides additional SPL through directivy but at the cost of negative diffraction effects in comparison to a flush-mounted dome tweeter. To combat these issues, I then looked at waveguides which balance the directivity of a horn while exhibiting less horn-like distortion. A waveguided tweeter probably would work for this application; however, compression drivers still have a “harsh” reputation that makes them less suitable for high fidelity applications. The Morel MDT 37 turns out to be an affordable dome tweeter set back in self contained horn-loaded enclosure (See Figure 3). This tweeter has SPL capabilities of a PA tweeter with the aural reputation of a hi-fi transducer (Johnson, 2007). As an added bonus, the MDT 37 has an affordable and easily replaceable voice coil making it ideal for situations Figure 3: Morel MDT37 where some forgiveness is necessary. Crossover With a fairly large woofer and a tweeter that doesn’t extend too far into the midrange, picking a crossover point was simply a matter of keeping the audible breakup to a minimum. With a 2-way system there really doesn’t seem to be a good solution to avoiding a crossover around 2 KHz.