From: chrisc@gold.gvg.tek.com (Chris Christensen)
Newsgroups: rec.audio
Subject: Re: Bi-Amp vs. Bridged Bi-Wire
Date: 3 Sep 92 22:49:29 GMT
Organization: Grass Valley Group, Grass Valley, CA

In article <1992Sep2.180434.27506@jarvis.csri.toronto.edu>
smith@eecg.toronto.edu (Michael B. Smith) writes:
>In article <5130@gold.gvg.tek.com> chrisc@gold.gvg.tek.com
(Chris Christensen) writes:

>>IMHO.......(And in my personal experience) If you Bi-Amp with an electronic
>>crossover AND bypass the crossover portion (only) of the internal passive
>>crossover you would have better sound.  Any Zobel and or response
>>compensation networks should be kept in tact.  Failure to remove the
>>passive crossover will reduce the effectiveness of the change to
>>electronic b-amping (but not eliminate it,  it is still the best way
>>to go).

>>Oh and electronic bi-amping is far superior (if done correctly) to the
>>"other" style of bi-amping where one uses two amplifiers and feeds a
>>full range signal to both LF and HF sections.

>So, active cross-over between pre-amp and amp, remove the passive
>cross-over in the speakers (somehow); hopefully this is available
>in good quality speakers.  

I would tend to believe that some knowledge of passive speaker
crossover design would be required to sucessfully know what to disable
in the crossover and whet not to.  see your question below :-)

>What is a "Zobel" or response compensation network?  I'd guess its
>an E.Q. type device to compensate for speaker non-linearities??

A Zobel is a simple network that helps to compensate for the imprdance
bump of a driver at resonance.  It's selection is somewhat iterative
based roughly on the frequency of the bump and it's Q.

I also talked about frequency response compensation networks,  some us
'em some don't, some need to and some won't!

If you are lucky the speakers will, have a simple symetrical crossover
and bypassing will be simple.

>>>(This comes from planning a pro-logic system with 10 amps and 5
>>>speakers, and wondering what to do with all of the extra amps...)

>>I hope that you will be using some of the power for a subwoofer!
>>And I hope that you will be able to use a center channel speaker  that
>>is identical to the Left and Right speaker!

>A sub is planned for the future.  For now, the speakers I'm planning to
>get have a 3dB point of 37 - 21 kHz.  Adequate for a start, but a Velodyne
>will be called for in the future! As for your center channel comment,
>I've heard this quite often.  I presume this in terms of wattage and
>sound quality?  If its under-powered, the voices will not be heard. 
>Is this what you mean?

What I mean is that the sound for the movies you will be enjoying with
this system are mixed on systems that use discrete identical speakers
for Left, Center and Right.  To accurately hear what the sound
designer intended requires a system in that configuration.

For estetic reasons people don't use center channel speakers or use
limited frequency bandwith speakers.  While the limited bandwith
speakers help with dialog clarity in busy mixes,  I believe the best
system uses all full range speakers with a subwoofer.

Exception is the surround speakers.  While they don't need to be
identical to the main speakers the surround effect will be the most dramatic
if they closely match the frequency response and phase response of the main
speakers within the pass band required for the suround channel.

Remember that the surround effect is created bu the selective
amplitude cancellation between the surround speakers and the main
speakers.  A clearer defined surround effect will be the result of
this careful selection!  In spite of the hype about ProLogic remember
That the best effect is achived with this cancellation effect.  The
steering logic can enhance but the basic acoustical needs must be met
first.

The cancellation effect I speak of is like this, and based on simple
surround without Pro steering logic.  The electronic encoding matrix
is the determining element.  All figures quited are therotical
maximum.

1.  The cancellation between the Meft main and Rignt main is infinity.

2.  The cancellation between the center channel and the Left or Right
main is 3 dB.

3.  The cancellation possible between the Left Main/Right Main and
the Surround speakers is 3 dB.

4.  The maximum cancellation possible between the center speaker and
the surround speakers is infinity!

Stering logic helps increase the 3 dB effects of case #2 and 3 but
must do so without affecting the "stereo" image from the Left main and
Right main speakers.
Oh and if you use an identical speaker for the center channel the
system will have better bass when reproducing commom bass signals!

-- 
Chris Christensen                  The opinions I express are my own,
chrisc@gold.gvg.tek.com            and sometimes they are wrong!
916-478-3419 FAX 916-478-3887      After all, I *AM* only human.