Currently putting the finishing touches on my Brother's "contraption". It is a mirror imaged array of 12 drivers in twelve sealed tubes that is actively quad-amped. All the drivers for the mains are made by Morel and consist of two 9" woofers, two 5" mids and one 1" soft dome per channel. If you can picture a pair of Dunlavy SC IV's but with each driver in it's own sealed tube instead of one large box, you'll have a good idea of what it looks like. We did this to minimize crosstalk and internal pressure from driver to driver, minimize internal standing waves, minimize baffle area in terms of improved imaging with reduced diffraction, add versatility in terms of driver spacing and mounting depth, etc...
The tubes are industrial grade PVC that are just big enough in diameter to fit each individual driver. Each tube has been lined internally with a "black hole" type substance and then loosely stuffed with fiberglass. The exteriers have been carpeted. The mids and tweeter baffles are covered with felt. Each tube has been wired with twisted pair conductors of varying gauge. The gauge selected varies with the frequency range being covered. The Q for the woofers has been kept around .5 for best transient response.
The other two drivers are downloaded subs in their own very large tubes ( slightly over 9 cu ft each ). The tubes for the subs came courtesy of AA's "Magnetar" aka Mike Bates. He used them in one of his earlier projects but went in a different direction. Each tube houses a very long throw ( 30 mm peak to peak ) dual voice coil 15" woofer. Q for the subs has been targeted at .7, which is still very tight and fast but not overly "dry" sounding.
As you might guess, this is a rather ambitious project and we are learning a LOT as we go along. One thing that we've found for sure is that the difference between passive crossovers with passive multi-amping and using active crossovers is a MASSIVE difference in sound quality. Like going from a Fisher Price "Close n Play" to a killer stereo. Keep in mind that the "passive crossovers" were VERY minimal and that we are using the same amps.
If you're wondering how much juice is feeding al of this, we are powering the system with the following. Everything is crossed at 24 db's per octave courtesy of a Marchand Deluxe crossover.
tweeters : 105 wpc 3KHz & up
mids: 220 wpc 400 Hz to 3 KHz
woofers: 400 wpc dual mono 60 Hz to 400 Hz
subs: 400 wpc dual mono 60 Hz & down
All of the amps have been highly modified i.e. rewired, fuses bypassed, upgraded caps, additional transformer for the woofer amp, larger transformer for the mid amp, etc...
We've built quite a few speakers before this and heavily modified quite a few others. Most have come out phenomenally well, especially given the costs involved. I've got a few more speaker projects to do when we are done with these. Some are for my personal use ( some E-stat's and a horn design ), some are for friends ( a LARGE line array, a few subs, etc.. ) and a few are for pro sound reinforcement ( full stacks with hardware to "fly" the high / mid cabinets ) for a local band.
As to why we do it, it is GREAT fun, a challenge and FAR more economical than buying something equivalent that was commercially produced. When you see what you can do with $100 in drivers, wood and wiring with the right tools and test equipment, it makes you want to "throw up" when looking at most of the commercial designs out there. Luckily, "most" of the homework has already been done by others that are far more knowledgable than any of us doing this. Most of it is just a matter of reading, following directions, applying theory and then breaking out some elbow grease and tweaking to get things "right". Besides all of the "fun" and learning involved, there is a GREAT amount of pride in doing things of this nature when all is said and done. Sean