Posted by Mark Weiss, P.E. [ 70.135.218.164 ] on June 26, 2006 at 03:03:10:
With David Lee’s permission, I am posting part of an e-mail discussion I have been having with him about driving the ZR-18 subwoofers and strategies for compensating for various mechanical damping levels at various frequencies above the vent tuning frequency.
I have two ZR-18 drivers in each vented box, a total of four. I would think the Z-min would occur at the box tuning frequency, in this case, 18Hz, where the mechanical resistance to displacement is the greatest. My concern at the moment is to tailor the response curve such that power is reduced at twice that frequency, keeping mechanical excursion under control within the frequency ranges where system damping is minimal. I know the suspension system is robust, but I don’t want to abuse it. I haven’t smelled any smoke at all. (In the past, my EVX180Bs have given off a formvar odor, but a tech from E-V tells me that’s normal during break in, and I was running them well below rated power when that occurred, strangely enough).
I may look into a series of limiters of the variety that allow independent adjustment of attack and release times, and try to anticipate thermal factors in setting it up. For the subs, a 1S attack time, allowing the leading edge of the transient at full power, but dropping back by -3dB after 1S, so as to avoid excessive heating. For mids, a much faster set of timings, allowing just the duration of a snare drum attack transient, and then reducing power to protect the JBL E120s that are used in midrange. (I’m exploring CGN’s meter ribbon line array modules as a possible next generation replacement for these vintage drivers in the near future, but am actually quite pleased with the JBLs in the cabinets I’ve designed to tailor their response for a smoother, extended low midrange end. Since Dec 2005, I’ve really done a lot of work on this system. It had remained pretty much as-is since the last update in 1984. Believe it or not, I still have gear from 1977 in the rack!
I’m pondering the design of new sub-bass cabinets, based loosely on the Wilson XS subwoofer, which is a box of close to 40 cu ft with an F3 down around 10Hz or so. One of the design goals is to reduce vent velocity, be able to increase vent area (to increase the vent’s contribution to overall SPL) and lower system response still further. The Wilson, which uses two Aura drivers, and large round ports not unlike what Carlos Beltran is selling, is a behemoth system—too bad it’s drivers only do 1.5” of excursion though. But I’ll need to do some research into ways to make the vent do more of the overall sound production, since the response from the vent is the flattest and extends the lowest.
I’m glad David is getting calls about these drivers based on my web site. www.basspig.com. I hope he sells many. They are a well-kept secret, with many audiophile applications. These are also an audiophile’s wet dream, but an audiophile’s wife’s worst nightmare. 
I’ve had some visitors from California in here last week, when I had only two Bassmaxx drivers installed, and running on only a single Hafler 500. I thought they were going to have heart attacks when the close-miked kick drum slammed us all in a beautifully-recorded Korean song that I played for the demo (a downloadable clip of it is on my May 21st blog and is quite a listening experience on a serious set of subs). I’m becoming increasingly concerned about lawsuits, so I have to exercise a great deal of self control when running a demo for a guest. A lot of folks just aren’t prepared for this kind of thing. These guys were somewhat critical of me, asking why I had to have so many speakers—they felt that one sub was more than enough. But they did mention that the vibration had a great laxative effect! Fine. To each, his own. For me, this is like a drug addiction—I have to have more and more as I develop tolerance.
I have a growing collection of 24/96 recordings, that I myself recorded, of various man-made and natural events such as fireworks, thunder, aircraft, etc, that I am using in certain demos. I’m also working out the details with an orchestra union to get exclusive recording rights to a symphony concert here in the state soon, so I am gradually creating my own library of 8-channel recorded events.
I can’t emphasize enough as to how CLEAN these drivers are—the fiberglass is like a perfect piston—it doesn’t flex or give at all—it just follows the input waveform faithfully and that difference was so glaringly obvious in Wednesday’s test. Just about every other driver on the market uses some derivative of a paper cone, and paper flexes in all sorts of undesired manners. It might make a good “musical instrument” speaker that gets loud with 10 watts input and has a particular sonic signature, but it’s not high fidelity. The cones are what made me choose the Bassmaxx over the Accoupower drivers. And David’s were a darned good deal. Did you know that my EVX180Bs increased to $549 each shortly after I bought mine? The two simply are in different leagues.
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