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From: billt@chips.com (Bill Tuohy)
Newsgroups: rec.audio.high-end
Subject: Quasi-second order crossover
Message-ID: <9528@uwm.edu>
Date: 13 Feb 91 14:07:27 GMT
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Approved: tjk@csd4.csd.uwm.edu
Originator: tjk@csd4.csd.uwm.edu


I am planning to build my first set of speakers, and
in my research I have come across a line (VMPS kits)
that use what they call a quasi-second order crossover.
I have not seen this term anywhere else.  It claims
to keep the same phase relationships as a first-order
network, but with steeper rolloffs, or something
along those lines.  It also said something like
using 6dB slopes for the low frequencies and 12dB
for the highs.     

Does anyone know exactly what this is?  What exactly
does such a circuit look like, maybe I can figure out
for myself what it does.

While I'm at it, I have another question about my design.
I was thinking of using two 5 1/4" midrange cones per
speaker, for increased power handling, but am unsure
how to connect them.  I think I would like to keep the
impedance at a nominal 8 ohms.  My first thought was to
connect two 4ohm drivers in series, but then I read that
series connections can cause problems if the drivers don't
match exactly and the amp has a high damping factor (or was
that a low damping factor?)  Anyway, if I connect two 8ohm
drivers in parrallel, the impedance is 4ohms.  Can I put
8ohm resistors in series with the drivers, making it a parallel
connection of 16ohm drivers, giving 8ohms?  If I have an L-pad
for the midrange, should I leave the parallel connection at 4ohms
and adjust with the L-pad?  My Carver amp recommends using only
8ohm speakers when A and B speakers will be used together.  I guess
the A and B are connected to the amp in parallel.

Is there any other benefits or problems with using two midrange
drivers like this?  I assume that dual-woofer theory applies
to base-mid cones as well.  Would two drivers give any better
imaging or anything, or should I try to find a single driver 
that can do what I want power wise?

Sorry for all the questions, but as anyone who has designed speakers
knows, there are a lot of variables.


Thanks,

Bill