From: Richard d Pierce <DPierce@world.std.com>
Newsgroups: rec.audio.high-end
Subject: re: Direct Drive ESL
Date: Tue, 13 Oct 1992 16:42:24 -0400 (EDT)
Organization: University of Wisconsin - Milwaukee
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Originator: tjk@csd4.csd.uwm.edu

And on the battle rages!

>As I wrote in the latest article, my models DO predict the known reality,
>the excessive current and threatened stability, very well. The models are
>good enough when they account phenomena that we are interested in. They
>should not be blamed because they can not account ANYTHING Mr. Pierce
>want. 

No, you have conceded that your model fairly well fails in its attempt to
predict the actual impedance. If I recall, you admitted that
your impedance model does not reconcile well at all with the actual
measured impedance. I submit that, therefore, the model is flawed. Period.

As to the "excessive current" and "threatened stability," these are both
assertion that you have made without submitting proof, as I stated in my
first reply. You have not provided, nor have we seen, any actual
measurements to support either the excess current or the instability
problems you suggest. I have sold, serviced, designed, measured, listened
to several thousand combinations of amplifiers and speakers over the past
20 years. Yes,, some amplifiers (of generally poor quality and
unacceptable design) have shown instability problems with electrostatics,
but they also showed instability problems with dynamic speakers as well.
So what, a bad amplifier is a bad amplifier. If you're amplifier has
instability problems, then fix the amplifier! The power amplifiers that
would normally be combined with electrostatic loudspeakers, as a rule,
show no signs of the instability you suggest.

In the absence, therefore, of evidence supporting this claim, I would
siggest that your model is flawed.

Again, the somewhat vague point about "excess current" is also made in the
absence of physical evidence. Have you measured currents of this
magnitude. While you model may predict them, the validity of your model
remains challanged by the lack of physical evidence. Both the pectral
characteristics of music and the efficiency characteristics of the speaker
weigh very much against your assertions.

As above, in the absence of supporting physical evidence supporting this
claim, you model is flawed.

>We should recall the history of 'trnsformer elimination'. It is never
>"easy" one. In the times of tubes, designers could not eliminate them till
>SEPP concept was established and low rp, high parviance tubes were
>developed. SEPP tube amps still have problems in the way of driving power
>tubes. Even in the age of transistors, designers used transformers for
>long time.

The anount of time the world spent with equipment that had any pretenses
of quality (let's say names like McIntosh, Marantz, etc.) that had solid
state devices with transformers was very brief. For Marantz, the duration
was precisely 0 days. For McIntosh, amps like the 2105 had autotransformer
outputs were part of the product line for a decade, but that was a
commmercial choice, not a technological one. Your statement that
"designers used transformers for a long time" is wrong. Now there were
several lower quality receivers and integrated amplifiers of both domestic
and foreign manufacture that dis use them, but they appeared around 1963
and had all but vanished from the market within four years. Two examples
are Pilot and Fukuin (prdon my spelling, if it's wrong), now Pioneer. Both
of thes units used transformer interstage coupling at a time when others
had already figured out how to do without it. In fact, the original AR amp
did the same.

>They only managed to eliminate them in the end of 60's and
>completed in early 70's as direct coupled, pure complimentary, SEPP OTL's.
>In this arrangement, they, at the first time, can feed back the output
>signals at any rate they like and, then, the problems of pass band width
>and nonlinear distortion both in amplitude and phase ultimately solved.
>Without any doubt, the most tough obstacles to solve the problems were
>transformers. 

I'm not sure I quite understand what you're saying here, but if
I understand the gist, you assert that the toughest problem to solve was
the transformers. Knowing,as I do, many of the people that, in fact,
solved many of these problems, including transformers, I would say that
this assertion is way off base.

>Thus, talking on eliminating transformers can not be called 'pissing off'
>unless Mr. Pierce wants to 'piss off' the whole history and whole effort 
>ever made for eliminating transformers.
>
>Even Mr. Pierce really thinks that it is easy, it is nice strategy to
>solve easiest problem first, isn't it?

No, in fact, it's a real dumb idea. I have witnessed more projects that
failed because of a deliberate strategy of solving the easy parts first,
the leaving the hard parts till there's no time left. The analogy holds
here quite well. I think you have a far more difficult time solving the
problems of the transducers themselves. My point was, and still is, once
you've eliminated the transformer, then what? You have the most difficult
path ahead of you. Having solved the transformer problem has no left you
confronting the issue of whether or not ESL are inherently superior,
desirable or even implementable.

The fact is that other have discovered what you seem to be taking a lot of
effort to avoid: that the transformer is NOT the biggest problem of ESL's
and thus should remain a problem which can be easily defered. Again I ask
the question: why ESLs? What do you gain? What do you loose?

Reconcile your model with real observed reality, not your assumptions of
reality. Show me a close correlation between the predicted impedance curve
of an ESL using your model and the real impedance curve of an ESL. SHow me
the high current levels at low frequencies that you've measured and how
they are predicted by your model. Show me a modern day amplifier on the
verge of instability (or actually unstable). SHow me the evidence and I
will be more inclined to accept the validity of your model.

Until then, I'm afraid your models aren't worth much.

The models I use predict measureable reality very, very well. The
impedance curves of a complex, multi-way loudspeaker are typically within
2% of the measured impedance. The frequency response is often with
measurment accuracy. So I would argue my models work. Yours may work, too,
but you have failed to produce the supporting evidence.

Without the evidence, your models loose.

|                Dick Pierce                |
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