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Old 5th December 2009, 04:19 PM   #1
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Default MTM, Two woofer formula?

I want to design an MTM "tower" with two 15" drivers & a horn in the middle ala DeAppolito type.
I came across this driver, 15",Fs=42Hz,Vas=8.6cu FT, Qms=4.73, Qes=.44, Qts=.4, Db=101.6 @1W1M,

I ran the formulas & came up with Vb=9.3004...., F3=39.385...., Fb=40.238....
The thing I don't have is the formulas for twin drivers in a tuned box.
Is there a hard formula for dual/multiple drivers?
The application is for a very low powered tube amp......I'm shooting for 104+ Db response. I know it can be done, I've just come to this impasse.

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Old 5th December 2009, 04:37 PM   #2
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Just double box volume and use two ports as they would be in a single box.
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Old 5th December 2009, 04:44 PM   #3
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You can use the same formula for 2 identical drivers using T/S for the single, with the only difference being Vas is doubled. Your tuning of Vb~1/2(2*Vas) is about right for the double.
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Old 5th December 2009, 05:32 PM   #4
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For modelling purposes, if the twin drivers in parallel, Sd & Vas effectively double compared to the single unit, while Re & Le are halved. If the twin drivers are wired in series, then Sd, Vas, B*L, Re & Le all nominally double compared to the single unit.
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