From: Richard d Pierce <DPierce@world.std.com>
Newsgroups: rec.audio.high-end
Subject: RE: Direct Drive ESL
Date: 28 Sep 1992 13:08:36 GMT
Organization: University of Wisconsin - Milwaukee
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Originator: tjk@csd4.csd.uwm.edu


Several people have written to me to correct a statement that I made in regard
to the ongoing discussion of the relative merits of transformer vs. direct
drive electrostatic loudspeakers.

I stated that the ESL units that I was familiar with did not have the
series resistances in them that Mr. Motoyama stated they did. It would
appear that my memory may well be defective, as several of the respondents
pointed out that they had specific knowledge that certain units did, in
fact, have such resistors, typically in the region of 4 ohms or so. 

Well, clearly my memory of events and facts regarding this particular
subject is waning, and I got it wrong. So I apologize for my misstatements.

However, this does not invalidate the remainder of my points. The fact
that the resistors exists or not in actual fact does not invalidate my
points in objection to Mr. Motoyama's "naked" circuit element concept. 

The effect is quite the same as the DC resistance of the voice coil in
normal electro-dynamic drivers, along with the whopping equivalent circuit
values for the driver compliance, mass, and so forth.

Let's move the discussion forward a bit. Mr. Motoyama seems to have
focused on one particular aspect of transformer coupling that frankly does
not have a whole hill of beans to do with reality. There are whole legions
of problems with transformers, non-linearity, bandwidth limiting, etc.,
that  frankly are far stronger arguments for condemning there use. 

Frankly, stability was never a problem with the kinds of amplifiers I
typically sold for electrostatic use. So why beat the issue to death.
I will readily agree with Mr. Motoyama that transformers are, in general,
lousy ways of soupling wide band signals with minimal perturbations. 

Now, let's eliminate the transformer and substitute a direct-drive
amplifier. Great! What have we done? Well we've substituted transformer
problems with direct drive amplifier problems. Several of the respondents
also pointed out the those ESL units that did have direct-drive amplifiers
also suffered a whole set of problems of their own. The Accoustat system,
for example, had to have whopping amounts of EQ inorder to work properly.

But let's go one step further: Let's say we can make either the
transformer coupled version or the direct drive version work perfectly, no
problems whatsoever. Now what. Well now we have to deal with the whole
list of problems with electrostatic transducers.

As a serious question, what is it about the electrostatic concept that
makes the above excercises worth it? (actually, this might be classified
as a serious rhetorical question!). Are we dealing with real advantages
here or simply preconceptions? 

I think, given this viewpoint, Mr. Motoyama has the cart before the horse.
He has seemingly presumed that the problem with conventional electrostatic
speakers is the transformer. Well, that's only partially true. The
transformer/amplifier issues merely deal with the electrical side of the
problem. Let's see if the acoustical and mechanical side of the issue is
sufficiently tractable to make the other side worth worrying about.

|                Dick Pierce                |
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