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From: km456265@longs.LANCE.ColoState.EDU (Kevin Melsheimer)
Newsgroups: rec.audio.high-end
Subject: Re: Subwoofer Building
Message-ID: <11040@uwm.edu>
Date: 15 Apr 91 12:34:31 GMT
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As to your first question:
1)  Has anyone had experience with Parts Express? Are their drivers and
crossover decent? How are their prices?

I have personally ordered many times from Parts Express and they are a
reputable company.  When you call their 800 number you can expect to see
your order in no more than two weeks, one week usually being the case. 
I have found that their quality is good to excellent, the latter being
attributed only to their line of Polydax speakers.  The prices are
compared to many other mail order houses, but their sale prices have yet
to be topped by any mail order firm that I know of.  I don't have any
experience with their crossovers; but my friends that have ordered them
have been quite satisfied.

As for your second question concerning using a tube as an enclosure for
speakers, I have looked at this method for building speaker boxes and
have dismissed it due to the length of tubes required to tune subwoofers
properly.  With the 15" Thruster woofers I am currently using it would
be impossible to fit a properly tuned 15" tube within the length of any
room in my house.

Your third question asks about speakerboxes.  I currently am using a box
of 11.3 cubic feet with a tuned port of eighteen inches in length and
eleven inches in diameter.  This tunes the box to around 29 Hertz and
the frequency cuttoff for the box is about 28 Hz.  My box is made out of
3/4 inch plywood and I would recommend going with inch thick plywood if
you can afford it.  Bracing is also very important in a subwoofer
enclosure.  I use two x twos throughout the structure of the box, which
I might add is quite big.

As to your fourth question of having a crossover before your amplifier,
yes it is possible.  I am currently using a 100db per octive active
crossover crossed over at 112 Hz.  If your would like more information
on active crossovers and speakerbuilding in general, I would advise you
to read "Enhanced Sound:  22 projects for the audiophile."  It is my
opinion that this book is the most comprehensive book on Audio that
exists for the beginning audiophile.

Your fifth question asks about dual-voice coil subwoofers.  These units
sole purpose in life is to be driven by an amplifier that fails to have
the capacity of beign bridged into mono.  I would not recommend using a
dual voice coil woofer if you are a true audiophile.  The bass will get
quite distorted if the bass from the two channels being input are
different from each other.  This is due to the speaker trying to go in
two directions at once--the net result is distortion.  Dual voice-coil
units do have one practical use though.  If you own an amp that can put
power into two ohms, you will find that you can wire the woofer in
parallel (if the speaker was originally four ohms) and have a lot more
power available from your amp.

In your fourth question you ask about matching speaker efficiencies. 
This is important if you are driving the subwoofer off the same amp as
your main speakers (your Boston Acoustics A60's).  I would not recommend
doing this, however.  A subwoofer requires a lot of power and if you
want to use an active crossover, you will be forced to use another amp. 
Matching efficiencies are unimportant when you can control the amount of
power going into each speaker.  If your subwoofers are more efficient
than your A60's (which will probalby be the case) you can simply put
less power into them to compensate for this.  The speakers I would
recommend to you for building subwoofers would be the Thruster 12" found
in Parts Express.  This speaker has a very good frequency response if
ported properly (down to 18 Hz).  The box size will be quite large,
however.  Using a box size of 10.8 cubic feet will provide a speaker
that has no dips or peaks larger than +/- .5 dB under 150Hz.  If you
have the space, I would go with these.  I have found that the Thruster
line of speakers have the best sound quality for the price for woofers
(For bass-reflex applications).  If you find a better speaker for the
money, please notify me.

I hope you find my information usefull,
write me if you have any more questions
on subwoofers,

Kevin Melsheimer
km456265@longs.LANCE.ColoState.Edu