The Cabinator

[drmcclainphd]

I'm always trying to stretch the envelope when it comes to sound reinforcement. I try to get the most sound and highest power handling in the smallest space, and for the least amount of money. This is my best so far.

Start with 6 panels of ply, MDF, whathaveyou, 24" x 24". Use 4 to build most of a cube -- top and bottom held together by two adjacent sides. Cut off the corner of the top and bottom opposite the joint of the sides, at a 45 degree angle so the hypotenuse (the length of the diagonal cut) is 24". Take one of the remaining panels and install four 8" woofers. Drop it into the cube and mount it at a 45 degree angle between the sides. Take the other panel and install a 4 x 4 array of 5" full range drivers. Mount that where you cut the corner off the top and bottom. There will be an opening of 8" x 24" on either side. Hang a couple piezos on it for good measure.

The design is "detuned". Guitar amps are generally louder than stereos because they're usually opened in back. This fills the room with sound. This design closes the back and redirects the back side of the 16 drivers towards the front. Still lots of sound, but focused forwards. The side panels stick out more than the front (the 8" space) and are at 45 degrees to the front, so everything from rear side gets bounced straight forward, more or less, somewhat like a horn.
Here's some pics:
http://techtalk.parts-express.com/at...2&d=1321209481
http://techtalk.parts-express.com/at...3&d=1321209520
http://techtalk.parts-express.com/at...4&d=1321209546
http://techtalk.parts-express.com/at...5&d=1321209580

I used four Studio Pro WH-8 subs, and 16 of these wonderful little Sony speakers I've been picking up in bulk from Parts Express buyouts section for $2.50. Here's links:

http://www.parts-express.com/pe/show...60&FTR=290-260
http://www.parts-express.com/pe/show...number=299-011
http://www.parts-express.com/pe/show...number=270-011

Less than a full 24" cubed, about 6 cubic feet. 70 pounds. Wired in an 8 ohm network, it can handle 750 watts, but although the 5" drivers aren't extremely sensitive (SPL 85 dB @ 1m/1w) there's 16 of them so there's a whole lotta dB pouring out. According to some folks at DIYaudio, you get 3 dB for each additional driver. So after the first (85 dB) add 15 times 3 dB, 85 + 45 = 130. Then there's the woofers and horns. I kind of doubt the estimate for 1 watt SPL -- I'd say maybe 120. But keep in mind it's focused forwards.

I tested it at 500 watts with a Behringer iNuke 1000. I filled an entire drive in theater lot with sound, equal in intensity up through 45 degrees off axis. I turned it on its side and pointed it at the movie screen, and you could hear the vocals clearly a mile away. At the full 500 watts the Sonys held up fine. They tend to clack when over driven, but this network seemed to suit them.

I went a bit extra in this build. I usually try to keep a project down to $100 max. I got some handles for this since it's heavy and awkward, and I used rubberized undercoating spray paint to try to make it at least water resistant. It came to about $120., components, parts, supplies and finishing.

I've got a pair of towers based on the same shape and design, except they're based on 12" x 50" side and driver panels, with 12" square ends. They have 12 of the Sony's and two of the piezos each. The woofer is a pair of Peavey 12" subs installed in an old JVC home stereo speaker cab and vented in front. Besides being bridgeable for more power, the iNuke has a built in sub-out crossover. That test was an oh my golly gee whiz gosh sound party. It was probably the only time the cops came to a noise complaint at a drive in theater. But, it was broad daylight, and noise ordinance starts at 11 PM, and besides, I was playing along with Surfin' With The Alien and the deputy was a Satriani fan. The two towers plus the two sub drivers cost under $200 all told, and had I built a cab instead of hacking used furniture, would have been way less than $300 for the three. Total handling power for the three is about 800 watts and the same focusing plus detuned design plus multiple drivers puts the SPL over 130 when the bass is kicking.

[UncleLarry]

Wow, I just don't know what to say about that wild speaker array! But it's sure crazy enough for TGP. Guys like you keep this forum interesting!

[drmcclainphd]

The 4x4 array is an old hifi design, called The Sweet 16. Had its day in the 50s. Nowdays people try to claim multiple speakers cause interference inthe sound, a "comb filter" problem. They think a point source is best. There are no point sources. Every driver has the same problem -- sound comes from the whole think. The multiple drivers actually probably have less problem than "regular" designs because the combined output approximates a planar wave. What good is that? Take 47 of those piezos and mount them on a panel all pointed the same way. Run some high powered screechiness noise through them. You now have an LRAD, the military's Long Range Acoustic Device, ostensibly a communication system. But it has been used successfully to deter armed fighters and disperse crowds. It's a sonic weapon, and has quite a tight beam despite using high dispersion piezos.

[The Kid]

Crazy...

[drmcclainphd]

Originally Posted by The Kid

Crazy...

"Some say that I'm a wise man. Some say that I'm a fool.
It doesn't matter either way: I'll be a wise man's fool.
For the lesson lies in learning and by teaching I'll be taught,
there's nothing hidden anywhere, it's all there to be sought."

Or maybe I'm confusing that with a different Procol Harum song:
In the autumn of my madness, when my hair is turning grey...

[The Kid]

I meant crazy as in interesting / cool. It's pretty wild looking. I'd love to hear that setup. I wasn't calling anyone foolish. Sorry for any confusion.

[Jef Bardsley]

Forgive the good Doctor if he seems a bit touchy, he's been given a hard time on another board by one of the "gurus".

Originally Posted by drmcclainphd

The design is "detuned".

Mmmm.... I'd say it's a Sweet Sixteen array in an open baffle, backed by a reflector that includes a horn-loaded bandpass acoustic suspension woofer array. Actually, I'd write that.... I think I'd simply say, "It's complicated."

Originally Posted by drmcclainphd

Wired in an 8 ohm network, it can handle 750 watts, but although the 5" drivers aren't extremely sensitive (SPL 85 dB @ 1m/1w) there's 16 of them so there's a whole lotta dB pouring out. According to some folks at DIYaudio, you get 3 dB for each additional driver. So after the first (85 dB) add 15 times 3 dB, 85 + 45 = 130.

Well, to get that first 85dB you need to feed the driver 1 watt, so that's 16 watts to the front array for 130dB. Then, add +3 for each of the 4 drivers in the center (everyone talks about "coupling", but it seems few have read the white paper - it doesn't apply to the drivers on the edge), add +6dB to the low end for the 4 drivers on the floor operating in 1/4 space, add -6dB for the 4 drivers on the top edge due to diffraction, and the 8 drivers on the side will null giving the -6 dB curve of an OB (except there's that reflector), and of course all that is frequency dependent with varying turnover points..... some people seem to live to predict the output of a system, I simply bought an SPL meter back in '63. Much quicker and more accurate.


At any rate, I find your design fascinating, if not brilliant. Numbers would be nice, but anything important should show up in simple listening tests (says the guy with more audio test gear than guitars!).


Jef

PS: I'm assuming there's no crossover?