tri-amping

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Each channel (R or L) of the big amp will look something like this.

Each of the channels labeled - are out of phase, but the speaker is reversed so it runs in phase.
 

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ok so it appears that the drivers will either have their + terminal connected to the + terminal and receive an inphase signal or have their terminal connected to the - terminal connected to the + terminal and be fed an out of phase signal ....

As far as phase goes, this will work .... but why bother?

only practical purpose i can see in this is that you could later bridge the amps... but hopefully, you are not even considering this :) otherwise i cant see the point in making things more complicated than they already need be :)
 
I don't really plan on bridging them, but at least it could be done. :) If it was, though, the channels would probably be bridged and paralleled, to give 3600W into 12 ohms x 2. Also, with the channels out of phase with each other, when one channel is drawing from the + rail, another is drawing from the - rail, lowering peak demands on each half of the supply. I don't know if this will actually help with anything, but I'm hoping it will let me get away with fewer of those giant reservoir caps because the peak current will be smaller.
 
Looks to me like you are trying to do a PA with Autosound woofers (albeit very efficient ones), hmmmm. The LAB on www.prosoundweb.com is currently doing a PA Horn Subwoofer project http://staging.live-audio.com/forum.php?board=3 that might rival the mighty Servodrive BT-7 (incidently the designer of the aforementioned is participating in this venture, but it might still take a while before the design materializes). You can probably expect to get about 110 dB/1W/1m from these from about 30 Hz and up when stacked four a side but two a side should also do you good albeit with a little bit less extension at the bottom. The design goal is as much accoustic output from 28 Hz and up for the buck as possible (read big concerts and the like)

I doubt whether the system you mention will be able to handle the power you mentioned mechanically due to excursion limits and even if it does the power compression effects would limit the SPL you'll acheive cleanly.

Monacor sell a mid-horn (IMG StageLine MRH-650) that will give you a 111 dB/1W/1m efficiency and 250W continuous power handling and very good linearity) from about 600-700 Hz to about 8-10kHz and tweeter horns to match abound. This leaves the 200Hz to 700Hz region where you might have to construct a mid-bin and here I am rambling on about a 4-way fully hornloaded PA but this is probably the only way to go at the SPLs you are aiming at.

Now for the maths. 110dB/1W/1m + 35.6 dB = 145.6 @ 1m. This is a serious amount so say the least and should allow you to stage big events. The ammount you can expect for your currently envisioned rig is 138 dB not counting compression which I would expect to be at least 5 dB or more at those levels.

It might be advisable to use a variable x-over and while you are at it pop an EQ and a mixer into your 19" flight rack. BTW, 100 dB/1W/1m is not unheard of for a decent 15" PA speaker!

I am certain that many other options exist and you'd probably be best off by reading up on prosoundweb first.

Hope this helps

Martin Goedeke
 
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