The main inherent advantage of the full-range electrostatic loud speaker system is that it allows a single diaphragm to embody the conflicting attributes needed for optimal performance at both extremes of the audio range. Its thin-membrane diaphragm can be made exceedingly light, for superb transient response and extended HF response, yet it can be about as large in area as desired, for extended LF response. And since that diaphragm is driven uniformly over its entire surface, instead of from a relatively small voice-coil, it circumvents the inherent problem of dynamic speakers in requiring that a large area be driven from a small area (the central voice-coil). The electrostatic’s diaphragm does not require the element of rigidity in order to move uniformly over its entire surface. And because the same diaphragm handles both bass and treble, the electrostatic does not need a crossover, with its inherent phasing and audible discontinuity problems.
These are the reasons why designers have persevered for over 40 years in refining the electrostatic, despite its unenviable history of woes ranging from gross inefficiency, through “difficult” amplifier loading, to daunting unreliability. (Unlike dynamic speakers, which will handle momentary overloads with aplomb, most electrostatics will break down instantly the first time an overload hits them. The usual result—a small hole in the diaphragm—then becomes a point of vulnerability, which will from then on arc over at signal levels well below what the speaker could normally handle.)
Editor’s Note: While the problem with over-driving electrostatic speakers was true when this article was first published—I remember the late Peter Walker showing me a pair of Quad ESL-57s where the diaphragms had been completely burned away—modern designs, like the MartinLogans, are much less vulnerable to damage.—John Atkinson
Appendix: Eletrostatic Loudspeakers reviewed in Stereophile
Infinity Servo-Statik 1 loudspeaker, J. Gordon Holt, November, 1968
KLH Model Nine loudspeaker, J. Gordon Holt, June 1975.
Quad ESL-63 loudspeaker, J. Gordon Holt & Various, September, 1983.
Acoustat 2+2 loudspeaker, J. Gordon Holt, March 1984.
MartinLogan Monolith loudspeaker, J. Gordon Holt, March 1984.
Acoustat 2+2 loudspeaker J. Gordon Holt, March, 1984.
MartinLogan CLS loudspeaker, John Atkinson & Various, July 1986.
Sound-Lab A-3 loudspeaker, J. Gordon Holt, September, 1986.
Acoustat Spectra 3 loudspeaker, J. Gordon Holt, August 1987.
Quad ESL loudspeaker Dick Olsher, August 1987.
MartinLogan Sequel II loudspeaker, John Atkinson & Various, August, 1989.
Acoustat Spectra 11 loudspeaker, Sam Tellig & Thomas J. Norton, January 1990.
Acoustat Spectra 1100 loudspeaker, Guy Lemcoe, August 1991.
Sound-Lab A-1 electrostatic loudspeaker
, Dick Olsher, November 1992.
MartinLogan Quest Z loudspeaker, Dick Olsher, October 1993.
MartinLogan Aerius loudspeaker, John Atkinson, October, 1993.
Audiostatic ES-100 loudspeaker
, Dick Olsher, March 1994.
MartinLogan SL3 loudspeaker, Wes Phillips, May 1997.
MartinLogan Prodigy loudspeaker, Larry Greenhill, July 2001.
Quad ESL-989 electrostatic loudspeaker, Larry Greenhill, November 2002.
InnerSound Eros Mk.III electrostatic loudspeaker Larry Greenhill, April 2003.
Innersound Kaya Reference loudspeaker, Paul Bolin, December 2004.
Quad Reference ESL-2805 loudspeaker
, John Atkinson, May 2012.
MartinLogan Montis loudspeaker
, Robert Deutsch, September 2012.
MartinLogan Masterpiece Renaissance ESL 15A loudspeaker Jon Iverson, January 2017.
Quad ESL-2912 loudspeaker, Robert Deutsch, August 2017.
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