Post by e***@fuse.netJust to throw this out for a 25 + year old speaker. I have Acoust
model X with the servo amps. I have had (myself) the amps refurbished
with all modern parts. The frames and panels are original with the
exception of modern dampening and other tech. I go to homes with $30K
plus newer systems. I do not come home wanting more. My sound stage
is as good if not better, bass, and high frequencies are right there.
Any one reading these threads who has Acoustats, do not let them
divert your attention. They are worth the effort.
I don't doubt that many of them are very much worth saving. There is, after
all, something magic about electrostatic speakers. Most are push-pull design
and therefore are capable of much lower distortion than are cone speakers and
most planar dynamic designs (which are single-ended, being driven only from
magnets on the front side of the diaphragm). Also, electrostatics (especially
full range) tend to be very coherent from top to bottom since all frequencies
radiate from the same surface and they tend to be naturally time-aligned (in
the E.M. Long sense) for the same reason. If the power supplies are adequate
and the transformer is properly designed, they can be very satisfying. OTOH,
Electrostatics tend to be light in the bass, they tend to beam and many have
a very small listening "sweet spot" **. Older designs have very little
response at either the top or the bottom (the original Quads) and tend to
suffer from arcing (extremely high voltage is required for them to work)
caused by a curious electrostatic field effect known as charge migration
where all of the static charge tends to concentrate at the point where the
diaphragm comes closest to the stator plates (the perforated panels covering
the diaphragm on both sides of the speaker). This point is, of course, the
place where the diaphragm moves the most and that's its physical center. If
not compensated for, this phenomenon causes only the center of the speaker to
produce any appreciable sound, and of course, excess excursion here will
cause the aforementioned arcing which can actually punch holes in the
diaphragm.
Modern designs have gotten around these various shortcomings and good modern
electrostatics are very good indeed, but the further one goes back in time
with earlier designs, one is going run up on these limitations. For instance,
back in the 1970's a company called Beveridge made some very expensive
electrostatic speakers with dedicated tube amps. The plates of the push-pull
tube amps connected directly to the stator plates of the speakers, thus
eliminating the double impedance conversion needed with most tube amp powered
electrostatics. While the Beveridges sounded quite good for their day, IIRC,
they could hardly play above a whisper without arcing. Arnie Nudel's Infinity
Servo-Static electrostatics were quite spectacular - on those rare days when
all of the small panels that made up the speaker's incredible surface area
worked at once - something that many critics maintained was a statistical
impossibility. And then there were the original Quads, where it all started.
These quirky speakers had marvelous midrange but absolutely no bass below
about 70 Hz and no treble above about 6 KHz. I've seen hybrid designs in the
'70's where a large frame held two Quads per side (one inverted over the
other to form a continuous arc from top to bottom) with a Decca ribbon
tweeter mounted between them and a large woofer in a box at the bottom of the
frame (forget who made these things but they actually sounded really good for
the time. They were terribly expensive though, as I recall). Of course, who
can forget the Dayton-Wrights of the late sixties and '70's which got around
the arcing problems by encasing the electrostatic elements in a bag full of
some kind of inert gas (hexaflourine?) to allow for more excursion without
danger of arcing. Finally, the first few generations of Acoustat speakers had
many of the above problems and should be avoided for the reasons mentioned.
**I once reviewed a pair of Roger Sanders' InnerSound electrostatics that I
thought sounded very good. The problem with them was that they had me
seriously contemplating checking antique stores for one of those "head vise"
contraptions that you often see holding people's heads still in old 19th
century deguerreotypes! As a listener, you literally couldn't move your head
an inch without losing all the highs. Setting the speakers up required that
one use a flashlight atop ones head pointing forward so that the beam hit the
wall exactly halfway between the two speakers. Then, you had to toe the two
speakers in until you could see the reflection of the flashlight beam equally
in both metalized mylar diaphragms! As far as I was concerned, this was
unacceptable, irrespective of how good the speakers sounded when optimally
set-up, and they WERE very good indeed. Who wants speakers that couldn't be
shared with others? This is a problem with lots of electrostatics, although
probably not to the extent of the InnerSound experience. Martin Logan gets
around this by curving his panels and they have a much wider listening angle.
In fact the "sweet spot" in most MLs extends to more than 30 degrees
off-axis.