Posted by Duke [ 208.98.184.4 ] on November 14, 2007 at 17:40:41:
Several of you have expressed interest in a kit, and I've been hesitant because then any competitor who wanted to could just buy the parts I use and copy what I'm doing. Twice at audio shows I've had someone (apparently not from the U.S.) want to buy just a single crossover from me, which sort of sends up a red flag.
Well, there has been a slight shift in the prevailing winds, and a kit might become a possibility. You see, I have engaged A Brown Soun (Hemptone) to design a custom woofer for me. I have not yet received the prototypes, but assuming all goes well in the not-too-distant future I'll have one helluva sexy woofer that will be mine and mine alone. All mine, I tell you! Moo-hoo-haa-Haa-HAAA!!
The woofer will have a cast frame, beefy motor with Faraday rings, and a hemp cone (insert your own joke). The cone profile will be a custom one they're doing just for me, which modelling indicates should give me very smooth response up to a bit north of 2 kHz with minimal peaking beyond that. Efficiency will be in the 96 dB ballpark. Now normally a 12" woofer with that sort of efficiency doesn't go very deep, unless it's optimized for use in a huge box. My custom woofers will incorporate a very unusual feature (and ya'll are the first to hear about it): They will have two 8-ohm voice coils! One coil will be driven full-range by your amplifier, and the other coil will be "boosted" by a plate amp. This will give the possibility of very deep bass in a reasonably compact enclosure without your amplifier seeing a nasty impedance curve. The voice coils and motor will be designed to minimize the thermal effects of the extra wattage going into that second voice coil.
I had initially expressed a preference for an alnico or neodymium manget, but A Brown Soun's engineers told me that they could better meet my performance requirements with a ceramic magnet that used Faraday rings - and it would be less expensive as well (still they're more costly than JBL and close to TAD). Having heard their work in speakers offered by another manufacturer, I'm confident they know what they're doing so decided to go with their recommendation on the magnet type.
Being able to independently control the level of deep bass has a several advantages. First and most obvious, there's an additional degree of freedom in the box size/efficiency/bass extension tradeoff. While maintaining 96 dB efficiency and a friendly 8-ohm load as seen by our main amplifier, we can take a four or five cubic foot box down into the lower 20's or a one cubic foot box down to an honest 40 Hz - so this will be a very flexible kit, depending on what the builder's priorities and requriements are. The other advantage is room adaptability. Low-frequency acoustic effects vary enormously from one room to another and from one position to another within a room, and the plate-amp-driven second voice coil will give a great deal of adaptability in this area. Finally, if you want even more low-frequency room-optimization capability, a plate amp that incorporates parametric equalization can be chosen.
Since this woofer will be proprietary (meaning A Brown Soun can't sell it to anyone else), I could offer a kit without it being easy for a competitor to copy me. Now maybe I flatter myself overmuch with delusions of people wanting to copy my speakers, but hey we all have our little fantasies, don't we?
Let me know what you think of this woofer, and of the prospect of a kit that uses it.
Duke
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