Historical notes on electrostatic loudspeakers


Electrostatics were invented by a German in 1880, but the materials for the diaphragm were never good enough for quality sound reproduction.



Kellog and Rice did their work in the '20s. The diaphragm material they used was a pig's intestine burnished with gold leaf.


The ESL was the first system able to produce appreciable sound-pressure as the electromagnetic loudspeaker was not yet developped due to the fact that sufficiently strong ferro-magnetic materials were not yet available before 1930.However, the moving forces of electrostatic fields could also be used only, when the first stronger amplifier (vacuum tubes) was developped in 1922. And this was the chance for the first usable loudspeaker, the electrostatic loudspeaker. It was the engineer Vogt in Berlin, Germany who invented and built the first ESL which were even strong enough to fill cinemas in the year 1922.

The loudspeakers measured several square-meters and were built by the "Deutsche Klangfilm AG" An electrostatic loudspeaker developes sound-pressure by the movement of a very thin diaphragm, which carries a high-voltage charge and forms a condensor with and between 2 perforated electrodes, which in their turn are fed symetrically with audio-frequency of high impedance, i.e. very high voltage. And these were the basic facts that caused problems, at least at the time. There were no good insulating materials like PVC or mylar and so there were many arcing problems between the perforated electrodes and the membrane. Therefore it was natural that with the development of good ferromagnetic materials, the electrodynamic speaker took over more and more, although the sound quality of an ELS is quite superior because of its better transient response


Very early Andre Charlin also started work on electrostatic loudspeakers, receiving a patent for a push-pull electrostat 1926. Electrostatic loudspeakers started appearing all over the world between 1925 and 1927, but were mostly of the single-ended variety. In 1927 different models (for reproduction of the higher frequency spectrum) were suggested by, apart from Charlin, the Englishman C. Kyle, the German Eugene Reitz and the Japanese T. Kageyama. There were also several demonstrations by Slepian, Edelman, Kellogg and Voigt. In 1926 Andre Charlin got patents for electrostatic loudspeakers with three elements.


The German Hans Vogt presented a working push-pull electrostat at the Berlin Radio Exhibition. We are trying to establish whether Charlin or Vogt was the earliest documented inventor.


Bell Telephone Laboratories were working on a new high efficiency cone-type loudspeaker coupled to a large throat horn, which considerably extended the low frequency range. An entirely new design of electrostatic loudspeaker was manufactured by a Chicago firm, and actually installed in several cinemas. It gave good fidelity with low distortion, but was lacking in bass frequencies. Messrs Vogt and Engl also tried electrostatic loudspeakers in Germany, using three types differing in size in an attempt to get a wide frequency response.

Experimental electrostatic loudspeaker (1929)

At a radio exhibit in 1929, a man named Hall cornered representatives of Victor and other companies and described a revolutionary new speaker. Taking them to his home in St. Charles, Illinois, he displayed the first working electrostatic speaker, made of perforated sheet metal and rubber dental stock, and occupying 4 feet of floor space. The representatives were not impressed enough with it's sound to overlook the dangerously high voltage it required to operate properly.


Within a dome-and-cone world, that may sound like a notion which defies inviolable laws of physics. But it's not. Consider, if you will, that the first truly practical Flat Panel loudspeaker was manufactured 67 years ago in the U.S. by the Automatic Musical Instrument Company of Grand Rapids, Michigan. An electrostatic device used by the company in a coin-operated precursor to the modern juke box, this Flat Panel patriarch performed poorly by today's standards, but worked nonetheless, establishing a path for others to follow.


But others were slow in coming, if they came at all. As time passed, the further refinement of Flat Panel loudspeaker designs was stymied by cost. The materials required in the manufacturing process were simply too expensive to encourage a proper profit incentive. All that changed in the 1950s when the materials required to produce Flat Panel loudspeakers on a large scale became widely available at more reasonable prices. Built using a number of plastics and charged films, flat electrostatic devices appeared in number, among which the most famous was the Quad ESL 57.

Peter Walker (Acoustical Mfg. Ltd.) and David Williamson (Ferranti Ltd., Edinburgh) were designing and building the very first Quads. The Quad was a 'horizontal' design compared with Janszen's 6 foot high line source. The centre strip of the middle Quad (treble) panel was 11/2inches wide with a cutoff frequency of 7 000 Hz. The two mid-range strips placed either side of this strip in the same panel, but segmented (after Kellogg) from the central strip electrically. The bass panels were placed symmetrically on either side of the treble panel. The treble panel was charged to 1 500 Volts and the bass panels were charged to 6 000 Volts.

Peter Walker was tussling with the problem of electrostatic sound reproduction. How he latched onto this idea and clung to it so tenaciously is a mystery. The principal of an electrostatic driver was known in the 1920s but the limitations imposed by physics made it impractical to build. Maybe Walker heard a hint of the potential promised by the design around 1950, and set his sights on developing the speaker with single-minded determination.

It is rumoured that when introduced at the London Audio Show in the mid-1950s, the speaker we now call the ESL-57 caused many conventional speaker manufacturers to wonder how long they, themselves, would survive. "Walker's Little Wonder" was a remarkable achievement, even measured by today's standards.

But even with the availability of cheaper materials at a manufacturing level, Flat Panel loudspeakers remained the red-headed stepchild of the audio world. Still widely perceived--accurately or not--as esoteric and expensive, their demand on electronics and somewhat unstable nature at the time often made ownership an ordeal about as pleasant as the prospect of a vasectomy performed with a dull linoleum knife.


Around 1963, according to legend, Peter Walker set out, on his own this time, to improve on the original Quad ESL. His efforts as we know, led to the speaker we now call the ESL '63 (U.S. Patent 3,773,984). The unusual segmentation features of this speaker can trace their line of development directly to Kellogg's original G.B. Patent 346,646, and a comparison of the two patents reveals interesting similarities. The original AES lecture given by Peter Walker in September 1979, clearly refers to Kellogg's work in connection with the ESL '63.

mid-to-late '60s

In the late '60's Flat Panel Evolution takes a three-way split. Meanwhile, back in the mainstream audio world of the mid-to-late '60s, a wellspring of advancements were made in traditional loudspeaker design such as air suspension and the development of long-throw transducers. At this same time, the evolutionary path taken by Flat Panel loudspeakers diverged into a three-way split.

One group, including manufacturers such as KLH, Martin Logan, and Infinity opted to maintain a conventional high-voltage approach. A second faction, of which Magnepan was representative, decided to seek out ways in which energy could be created using magnetic materials. A third and considerably smaller band of individuals sought to construct Flat Panel systems from other types of materials to produce a reliable, cost-effective product capable of delivering true hi-fi performance.