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From: gstead@maestro.mitre.org (Graham Stead)
Newsgroups: rec.audio.high-end
Subject: Re: Subwoofer Building
Message-ID: <11039@uwm.edu>
Date: 15 Apr 91 12:34:17 GMT
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Approved: tjk@csd4.csd.uwm.edu
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In article <10976@uwm.edu>, cs004017@cs.brown.edu (Steve Liebling) writes:
|> 
|> I am considering building a subwoofer and I have a few questions:
|> 
|> 1)  Has anyone had experience with Parts Express? Are their drivers 
|> and crossover decent? How are their prices?

Nope, sorry. I've ordered stuff from Madisound and A&S Speakers,
and I much prefer Madisound.

|> 2) I read about using a tube for a subwoofer, but how do you set-up 
|> the woofer in a room?  Does it go with the woofer firing downward using 
|> short stands on which to rest the tube? Do you lie the tube on its side 
|> and have the woofer fire sidewides?  How about suspending the tube upright 
|> using string from a ceiling?  It seems that this method might better 
|> isolate the speaker from the room acoustically but might not be good 
|> for resonances. (I don't mean to be pretentious as to understanding all 
|> this, I'm  putting forth some possibly imaginative hypothesis).

I don't know if I'd suspend it from the ceiling. The driver and enclosure
wouldn't be coupled or "connected" to anything, and swing, bounce, or
vibrate in a way that's detrimental sound reproduction. The other 
possibilities would work fine, because the very low frequencies you're
reproducing should be omnidirectional.

|> 3)  What type of material might be good for an enclosure (if I opt for 
|> the non-tube type)?  Plywood?  How thick?

Most people use 5/8" particleboard. It's cheap! I read an article where a
guy built a box using aluminum and vinly siding - the box was great but
expensive.

|> 4)  What about amplification? I mean, the most efficient use of the 
|> subwoofer would be to amplifiy only the low end, but this entails, 
|> having a crossover before the amplifier stage, right?  How would this 
|> be possible?

True. You could build a dedicated amplifier (Velodyne, who make great
subwoofers, use a Class D because it only reproduces < 100 Hz. or so).
Then you would need an active crossover. But you can still use your
subs with a single amp: run the output into a passive crossover, with
the low output going to the sub and the high output going to your 
regular speakers.

|> 5)  What in the world is a double voice-coil driver?  Simply an 
|> electrodynamic transducer with two voice coils suspended in a 
|> cylindrical magnet hooked to a cone? Why two, and not just one bigger one?

I don't know how they're constructed...but in my experience they're
used for connecting left & right amplifier outputs to the same 
driver.

|> 6) If I use the same amp for my speakers (Boston Acoustics A60's) as for 
|> my subwoofer, then do I need a dedicated attenuator for the subwoofer to 
|> match the efficiency of my speakers? If so, would it go after the 
|> crossover or before?

I think "L-pads" are commonly used. It's common practice to
put them in series with the satellite speakers' signal because
they're typically more efficient and can be lowered to the
correct level.

-Graham