NetNews Usenet Archive 1992 #26/NN_1992_26.iso/spool/rec/audio/14664

Text File | 1992-11-07 | 2.9 KB | 60 lines

Newsgroups: rec.audio
Path: sparky!uunet!cis.ohio-state.edu!zaphod.mps.ohio-state.edu!darwin.sura.net!lhc!lhc!hunter
From: [e-mail] (Larry Hunter)
Subject: Re: Passive Bi-amping
In-Reply-To: [e-mail]'s message of 4 Nov 92 18:28:17 GMT
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Organization: National Library of Medicine
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Date: 5 Nov 92 19:13:13
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Ray Wakeland asks about bi-amping speakers that have a pair of terminals (one
for the upper range drivers and one for the woofers).  JJ (the curmudgeon)
calls these "bi-wiring" jacks and says:

 Yes, you can do that, BUT ... you will gain nothing from the most important
 features of bi-amping, those being 1) Freedom from overload being communicated
 across frequency, i.e. overload will happen (most amps being voltage amps)
 because of the voltage level, regardless of current, because the entire audio
 signal is present at both amp's output.  2) You gain nothing from the ability
 to make an electronic crossover, and use the various flexibilities one can get
 from having an active network with well-controlled impedences.

And Ray asks about Norm Strong's comment that "aftermarket" active crossovers
can be inferior to the installed passive crossovers because the original
crossover was designed for the particular drivers in the speaker, to which JJ
responds:

  It eliminates Norm's comments, but it also avoids all the positive effects of
  bi-amping, and requires two amplifiers anyhow.

Although JJ is basically right, he missed the possibility of getting the best
of both worlds.  I use a true biamp setup (active crossover & two amps) but
also take advantage of the "biwiring" jacks.  The biwire tap into the passive
crossover in my Duntechs is at about 300Hz (I forget the exact number, but for
the example, it doesn't matter.)  So I set the knee of the high pass of the
active crossover to about 250Hz (or whatever it actually is) at 18dB/octave and
the knee of the low pass to about 400Hz at 18dB/octave.  Each of these signals
gets sent to its own amp, gaining advantage (1) that JJ lists above -- awesome
power handling capability.  Then the amp outputs get sent to the appropriate
speaker terminals, where the stop band is just the difference between the
active crossover's output and the transition in the passive crossover, a
relatively narrow band.  This way, the designed passive crossover is still
determining exactly what the drivers see (as Strong suggests is a good idea),
but each of the amps sees only a reduced signal bandwidth (as JJ observes, the
main advantage of bi-amping).

            Larry
--
Lawrence Hunter, PhD.
National Library of Medicine
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