From: tonyb@juliet.ll.mit.edu ( Tony Berke )
Newsgroups: rec.audio
Subject: Re: Wanted to know bi-amp speakers advantages
Date: 6 Jan 93 20:57:05 GMT
	<1993Jan5.174202.1533@eafs000.ca.boeing.com> <C0Eq4u.BCE@world.std.com>
Organization: M.I.T. Lincoln Lab - Group 43


INCOMPLETE RESPONSE ALERT! INCOMPLETE RESPONSE ALERT!

In article <C0Eq4u.BCE@world.std.com> DPierce@world.std.com (Richard D Pierce) writes:

   >BUNK ALERT! BUNK ALERT!

   In article <1993Jan5.174202.1533@eafs000.ca.boeing.com> Mark J. Vandiver writes:
   >>>     I have a pair of m-1 mirage speakers. It bi-amp.
   >>>Can anyone tell me what's the advantage of a bi-am speakr?
   >
   >>Bi-Amping has many advantages, although hard to describe.

   >I should say, since you got enough of it wrong!

   [much deserved bashing deleted for brevity...]

   >>Gives greater control over equalization of speakers.

   >How?

   >There ARE good reasons for active crossovers, but you've failed to mention
   >any of them.

   >For example, there are classes of response functions that are
   >unachievable with passive circuits. This is probably the only real
   >advantage of active networks, but one that no commercial system takes
   >advantage of, to the best of my knowledge. It's not clear if these classes
   >of functions are useful to a particular loudspeaker application or not.

   >[more stuff deleted...]

OK, so the poor guy flubbed up pretty seriously.  But then you go on
to leave out most of the main advantages of multi-way amping yourself.
I'm sure you're aware of them, but left them out in the heat of the
moment.

First of all, the poster's assertion about biamping's reduction of
"phase distortion" might have been bogus, but biamping can certainly
reduce IM distortion in the amplifiers, for obvious reasons.

It wasn't mentioned, but multi-amping can, both in theory and in
practice, greatly reduce the odds of melting midranges and tweeters.
If you're going to clip the woofer amp, then there are some obvious
benifits to having the tweeter connected to an altogether different
amp.  I have a fair number of positive and negative examples of this
phenomenon from both my PA and home reproduction experience.

Biamping also has a well documented ability to mask much of the
audible effects of clipping in the low-frequency amplifier.  If one is
doing PA work, or likes to listen at dangerous volume levels, a
properly sized multi-amped system with a given total amplifier power
can typically produce higher SPLs from the same speaker components
than you would obtain by using a passive crossover and a single amp.

The guy went on to talk about (without using the term) the insertion
loss of a passive crossover, and pointed out that it's more fun to
pay for amplifier watts that get turned into sound then watts that
get turned into heat.  Dick's rebuttal to this was that the insertion
loss of a typical crossover needn't be so great.

I'd also be interested in seeing the numbers for the insertion loss,
distortion, and cost, of a really steep, really high-power, really
low-frequency crossover, say 60Hz, for those who want a subwoofer set
up that way.  I imagine that the inductors will either cost a lot,
saturate easily, be huge, or have high losses (most likely, a fair
portion of each).

Perhaps this is just a leftover from my PA roots, but in the sound
reinforcement world, midranges and tweeters are often MUCH more
sensitive than woofers, and a passive crossover might have to pad the
mids and tweeters a good 10dB to get things to match up.  Granted, the
bulk of the energy is in the bass, and typical direct radiator mids
and tweeters aren't all that sensitive, but the flame-ee did gave a
(potentially) valid point there.

I'd also like to point out that although computer modeling and
measurement tools are making passive crossovers much easier to design
and get *almost* right on the first try, the tweaking phase that adds
next to nothing to the final cost of a commercial speaker can, when
amortized over a single unit, be rather bothersome for the individual.
I'm convinced from personal experience that active crossovers can give
the home designer/builder of one-off systems a signifigant boost in
productivity, flexibility, and enjoyment.  These advantages, while
they might not be relevant to a commercial designer, are quite real to
the home-brew person with a finite time budget, to wit:

-you can pick the different drivers in a proposed system without
regard to their relative sensitivities (kinda handy when you want to
work with a specific driver or two for some reason -- like you already
have them lying around, perhaps ;-) ) This can be particularly
compelling if one is talking about trying to match a subwoofer to an
existing fullrange system.

-you can tweak the level, polarity, and phase (if you have the right
crossover) of each driver to your heart's content, without burning
through huge piles of polypropylene capacitors, funky coils, and big
resistors (that each take a week to show up from Madisound).  You
can also quickly evaluate the result of twiddling with the crossover
points in a system, and hear/measure the results pronto.  Again,
the cost factor is particularly relevant to subwoofer crossovers,
where the parts are large and expensive -- but tiny tweaks are
quite audible everywhere, and even if one can afford the parts,
the home-brewer using a passive crossover isn't likely to try them
all out, due to the sheer inconvenience.

Although I've never gotten around to building it, I've often
fantasized about an modular (active) "wonder crossover" board that
would have, in addition to the traditional features found in
commercial boxes, various jumper-selectable shelving, notch, etc,
circuits, assymetric slopes, spreading, etc.  Such a board would offer
the home-brewer a huge advantage in the attempt to optimize a sytstem
to work well in his/her own listening space.  While I'm not aware of
the exisitance of such a thing at the moment, the mere fact that one
can reasonably contemplate its creation says something about the
flexibility of active crossovers vs. passive ones.

As a bonus (only somewhat tongue-in-cheek) advantage:

-you can cludge together a huge pile of random amplifiers and impress
your buddies.  Of course, you'll never get to see them (your buddies,
that is), because you'll always be in your workshop making cables and
fixing amplifiers.

Happy twiddling,

Tony