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From: francis@chook.ua.oz.au (Francis Vaughan)
Newsgroups: rec.audio.high-end
Subject: Re: Subwoffer Driver Rec's Wanted...
Message-ID: <13096@uwm.edu>
Date: 14 Jun 91 12:46:40 GMT
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Approved: tjk@csd4.csd.uwm.edu
Originator: tjk@csd4.csd.uwm.edu



In article <13024@uwm.edu>, shimizu@unix.sri.com (Dan Shimizu) writes:

|> My cohort and I are on our devilish way to become speaker
|> designers and we're trying to design a pair of subs to go
|> along with some sattelite speakers we are building.  I
|> prefer sealed box designs, so I don't have to go through the
|> hassle of tuning and estimating Ql (box loss) that is required
|> for vented box designs.  My question is what is a good driver
|> to use for a sealed sub?  I just heard about the Audio Concept
|> 12" (AC12 Mk.2).  They sound good, does anyone have any experience
|> with these drivers?

There is little problem about Ql really. It is easily measured
by determining the final Q of your box after it is built.
You need a signal generaror, counter, amp, accurate resistor
and a DMM accurate at low frequencies (not hard). I would
always measure the final box no matter what, sealed or vented.
Stuffing in a sealed box is very important too, and the 
tolerances in both the driver you buy and the box you build mean
that it is very unlikley you will ever build a box first time out
that meets spec. Best trick is to build one to throw away (just
like software really :-). Choose a driver, and calculate the box
you figure you need, bang it together out of whatever comes to
hand. Make sure it is reasonably rigid and leak tight, but hey,
you can do this with no thought to cosmetics so it can be quick and
cheap. Measure the driver. Get your own TS parameters. (If you
decide on a sealed box, you will need to put a vent in the box
for some measurments, and later seal it up again. You can tweak
to your hearts content. You will almost always find that the box
volume is wrong. Build the box oversize and add junk inside to get
it right (heavy books are good, so are bits of wood). The stuffing
will make a big difference. Once it is right THEN build it for real.
Measuring the system resonances and Q for real are very
good guides to how it will perform.

Personally I prefer a sealed system Q of .707. Try a Dynaudio
30W100. Not cheap but very nice. Big too.

					Francis Vaughan.