The BassZilla Evolution (October 2003)
By Dick Olsher
This update has been finalized during October 2003, and summarizes the evolution of the BassZilla family over the past year. Two additional versions of the Lowther BassZilla are described below. It is expected that the design will be modified yet again in the next several months to accommodate a new 15-inch woofer. Sadly, Audax has discontinued the PR380M2, and while some stock may still be out there in dealer inventory, I expect the existing supply to dry up very soon. I have been investigating various alternatives, and the top candidate at the moment is the Eminence Magnum 15HO – a beautiful, made-in-the-USA, 15-inch pro woofer that is readily available. The 15HO should work well in the same bass enclosure volume, but with a higher box tuning.
Also expect to see a new Fostex-based BassZilla design by early 2004. Fostex has discontinued the FE208Σ in favor of a new single-cone driver dubbed the FE208EΣ. The new driver isn’t quite full range and needs help above 10 kHz. Therefore, the final design will feature a super tweeter to fill in the uppermost octave.
Early in 2003, Lowther had redesigned its twin cone driver. The inner cone now terminates in a ‘reverse roll’ or lip at the outer rim, which is said to smooth out the upper octave frequency response.
At the request of Jon Ver Halen, Lowther-America Club, I undertook a testing and evaluation program with the goal of designing a version of the BassZilla based on the new Lowther DX4. Jon was also concerned about pushing the DX4 hard in the bass. The problem is that the Lowther voice coil is limited to an excursion of +/- 1mm, and that is hardly adequate headroom below 100 Hz. I agreed to take another look at protecting the delicate Lowther driver from bass excursions. It has been argued by some designers that the Lowther represents the world’s best midrange, and that is should therefore be used in that role. Sure, that’s a simplistic argument that overlooks the issues of crossover networks and multiple driver integration. However, the concept of operating the Lowther as a wide range rather than a full range, was very appealing. And at the end, I settled for a frequency range of 150 Hz to beyond 10 kHz. In hindsight, I can say that once I found a sonically benign way of high-pass filtering the Lowther, the resultant benefits were nothing short of amazing. All forms of distortion were dramatically reduced, resulting in enhanced inner resolution, soundstage transparency, and harmonic textural purity..The sound could be characterized as full-bodied, sweet and relaxed, but I still wasn’t entirely happy with the treble quality.
The Lowther Diamond Edition
The directive to use the new Lowther DX4 as a wide range, rather than a full-range driver, has now been taken to its logical conclusion, and has given birth to the Diamond Edition. Yes, it’s the most expensive BassZilla version to date. For those of you who may balk at the substantial driver cost, stay tuned for the upcoming new Fostex design.
The Chinese Aurum Cantus G2Si ribbon tweeter is used as a super tweeter to fill in the top most octaves, from 10 kHz to beyond 20 kHz. As before, the DX4 is allowed to sing over its sweet spot, without pushing its excursion limits. The Lowther sound has been retained with a full-bodied tonal balance and world-class treble extension and transient response only an excellent ribbon tweeter is capable of. The Aurum Cantus tweeters are available from E-speakers: http://www.e-speakers.com/products/ac-ribbons.html
Note: The spacing between the tweeter face plate and the DX4 frame is 1 and 1/8 inches.
The Diamond Edition’s upper octaves are better defined and much more refined relative to the standard version. The sense of air and space is now nothing short of sensational.
Note: I am now recommending the use of the large Bybee Quantum Purifiers as indicated in the schematics. Check out: http://www.bybeetech.com/ and my article: http://www.blackdahlia.com/tipindex/Tip_38/tip_ 38.html The increased purity is well worth the expense.
Crossover network schematics for both the new DX4 version (without tweeter) and the Diamond Edition are available at no cost to original purchasers of the BassZilla kit plans. Simply email Dick Olsher at firstname.lastname@example.org to request the update. Everyone else will have to purchase the updated BassZilla kit plans to capture the latest chapter in the life of BassZilla. Purchase of the plans entitles you to all future updates free of charge.