Tip #65
Platinum and Diamond Editions Mk. II

by Dick Olsher


In the fall of 2007 I introduced Kevin Kerwin’s conception of the Platinum Edition. To quote from “Tip of the Month” No. 60 (http://www.blackdahlia.com/html/tip_60.html): “Every once in a while, something unexpected comes along. It’s the BassZilla’s family’s good fortune that Kevin Kerwin, an architect from St. Louis, decided to take up the DIY challenge of the Platinum Edition. Along the way, he refined the look and feel of the project. I think you will agree that his vision and execution of this project have raised the bar for the Platinum Edition. AutoCAD drawings were used for CNC cutting of the wood. I’m particularly fond of the woofer cabinet implementation, which of course also applies to the Diamond Edition. I was so enthusiastic about Kevin’s work, and since he offered to cut extra cabinets and baffles at the mill, I paid him to build me a set of cabinets and open baffles for my personal use.”

After a prolonged period of procrastination, I finally completed the assembly, mainly driver installation and wiring, and set out to test and evaluate the new woofer enclosure and Eminence Definimax 4015LF woofer. The bass cabinet as built by Kevin was lined on the interior walls with carpet tiles. These I left alone, but added acoustic foam (one sheet of 2-1/2" x 24" x 18” per bass cabinet, Parts Express part # 260-515) behind the woofer. Each sheet of foam was cut in two and wedged into the cabinet bracing behind the woofer.

The total net internal volume (exclusive of the bracing) is 4.72 cubic feet and the intended box tuning was 38 Hz with a predicted bass half-power frequency (F3) of 43 Hz. The measured in-room F3 was about 45 Hz in good agreement with the prediction. However, it became clear that the woofer’s low-pass network needed tweaking to mesh optimally with the Fostex 208EΣ. The revised network features a simple first order low-pass filter and results in a full-bodied tonal balance very much to my liking. Thus, the Platinum Edition Mk. II consists of the Kevin Kerwin style cabinet/open baffle together with the updated crossover network (shown in the updated kit plans).

In fact, I was so pleased with this BassZilla platform that I decided to use it to create a new version of the Diamond Edition. Thus was born the Diamond Edition Mk. II. Integrating the Lowther DX4 at a higher crossover frequency, necessitated by the smaller open baffle, made it possible to simplify matters and deploy a first-order high-pass filter.

Kevin Kerwin has put together a set of drawings outlining the construction of the Platinum Edition open baffle and bass enclosure, which he has graciously made available to all BassZilla lovers. These drawings are reproduced in the updated kit plans (dated November 2008) and are available free of charge to previous purchasers of the kit plans. Simply e-mail me - and be sure to include “BassZilla” in the subject header

I’ve noticed lately that I’m spending most of my time with the Mk. II Platinum Edition. This is no accident as its tonal balance and low-distortion spectrum facilitate long multi-hour listening sessions free of listener fatigue. The treble range is slightly shelved down with respect to the midrange, which makes for a middle of the hall spatial impression and an enhanced depth perspective.

Finally, let me thank all of the BassZilla fans who have provided me terrific feedback and valuable suggestions over the years. It is much appreciated and clearly responsible for the continued evolution and success of the BassZilla speaker family.