Newsgroups: rec.audio
From: smith@eecg.toronto.edu (Michael B. Smith)
Subject: Re: Bi-Amp vs. Bridged Bi-Wire
Organization: Dept. of Electrical Engineering, University of Toronto
Date: 2 Sep 92 21:52:45 GMT

In article <1992Sep2.115949.15983@irisa.fr> leconte@irisa.fr writes:
>In article 9571@jarvis.csri.toronto.edu, smith@eecg.toronto.edu (Michael B. Smith) writes:
>>Assume that you have speakers that can be bi-amped and you happen to
>>have four amps available.  One possible setup would be to bi-amp the
>>speakers (i.e. one amp for the left tweeter, one amp for the left
>>woofer, etc.).  Assuming that your amps can be bridged, it should also
>>be easy to hook these speakers to be only bi-wired, but driven by
>>a bridged amp.  This should provide about double to triple the power,
>>so they'll probably be louder.  But, the big question is, which version
>>should sound "better"?
>>  What are the merits of bi-wiring?
>
>Theorically none .

After hashing this out with some other grad students, we came to more or
less the same conclusion.  Sure, there is a more-or-less two-fold reduction
in wire impedance, but just decreasing the gauge should accomplish
similar results.

However, in the Summer/Fall 92 edition of "Audio Ideas Guide", page 8,
there is a letter from Christopher Russel of Bryston Ltd.  I'll quote
the important bits:

	Bi-wiring is an advantage due to the finite resistance of speaker
	cable, which is likely to be in the range of 10-100 times the output
	impedance of the power amplifier.  This cable resistance can allow
	distortion products to appear on the cable, and enter other drivers
	in the speaker.

	The reason this happens is that the impedance of a speaker voice
	coil is not linear.  Distortion products which appear in the motion
	of the driver will, through back EMF, modulate any resistance which
	is present at the source.  If those distortion products lie above
	the crossover frequency, they will become signals which cn be
	reproduced by other drivers in the same box.

	Bi-wiring more effectively blocks these distortion signals by placing
	the low resistance of the amplifier between the woofer, for
	instance, and the input terminals of the midrange.  This is a
	relatively subtle effect, but may be of interest in a refined
	system.

Sorry to blatantly quote a chunk of a mag, but I found it to be a good
explanation.  Whether or not anyone has witnessed this through a double-
blind test is a another question....  I'll have to experiment once I put
together my system.

>Bi-amping is more understood. The two amps see a less complex load.
>
>But if you have all these amps why not bi-amping with an active crossover ?
>The result will be  surely better.

I presume by this you mean using a powered filter between the pre-amp
and the amp to filter the highes out of the signal of the left woofer,
etc.  Yes, this would undoubtedly be better than the passive cross-over
in a speaker.  This will probably end up being a future up-grade!

Do you have any recommendations?  I'll probably only bi-amp my two main
drivers, and mono-bridge the effect speakers and center channel.  For
a sub woofer, even if I haven't yet planned one, I'll probably go for
a powered sub like a Velodyne.

Michael
-- 
--
Michael B. Smith					UofT:(416)978-1652
smith@picton.eecg.toronto.edu				Electrical Engineering
--
Time is a great teacher, but unfortunately it kills all its pupils.
From: kurts@hpnmdla.sr.hp.com (Kurt Strain)
Date: Thu, 3 Sep 1992 17:05:07 GMT
Subject: Re: Green Pens & CDs (was Re: Very expensive cables)
Organization: Outpost 1T