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From: hull%janus.Berkeley.EDU@ucbvax.Berkeley.EDU (Christopher Hull)
Newsgroups: rec.audio.high-end
Subject: Re: bi-amping
Message-ID: <8754@uwm.edu>
Date: 8 Jan 91 14:50:24 GMT
Sender: news@uwm.edu
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Approved: tjk@csd4.csd.uwm.edu
Originator: tjk@csd4.csd.uwm.edu

In article <8661@uwm.edu> you write:
>
>      I am interested in bi-amping by B&W 801s (currently bi-wired with
>Tara Return).  I have a lot of questions:
>
>1.  How much power is required for the tops (mid-range and tweeter) where
>the cross-over is, I believe, around 300 Hz?  I'd like to use a low to medium
>power tube amp (less than 100 watts per side).  How much is necessary?
>
>2.  Is an active cross-over required or can I simply feed the passive crossover
>already used for bi-wiring?  I have a dealer who says I need an active
>crossover if the top and bottom amps are not identical.  Could someone give me
>a technical explanation in more detail.
>


You can use a passive crossover, however that will negate most of the
advantages of bi-amping since both amps will have to deal with the whole
spectrum.  In that case both amps will need to be high powerd, especially
the one for >300hz, since its distortion will be most audible.

If you use a low level crossover (either electronic or passive, but before
the amps!) than each amp can be about 1/2 of the power you would normally
require.  If you are going to equalize your subwoffer than you would need
more on the bass amp.  I recommend that the high pass part of the crossover
be either passive or tube, since you will introduce audible distortion with
a solid-state x-over for frequencies > 300hz.  Unfortunately, the B&W were
designed for steep x-overs I believe.  If you want to use slopes > 6db/octive
than you will need to use an active x-over for sure.  In that case I recommend
tube x-overs or hybrids.

Chris Hull

hull@janus.berkeley.edu