All the following information comes from the review off the ESL 57 in the November 1957 edition of HiFi News. For the full review click here.
The concept of electrostatic speakers has been known about since the discovery of electricity. The first electrostatic speaker was designed by Dolbear. This device was incorporated into an electrostatic telephone system which was demonstrated at the Paris Electrical Exhibition of 1881. Electrostatic speakers continued to be made during the 1920's and 1930's mainly in Germany. In the UK the Primustatic loudspeaker was available for 25 shillings (£1.25). For the next 20 years the only electrostatic (ES) devices available were condenser microphones. Development of ES devices stopped during the 1940's and wasn't started until the mid 50's.
The main stumbling blocks to successful ES devices were the fact that the theory hadn't been worked out properly and the theoretically massless diaphragm couldn't be made from the materials available at the time. In 1954 Prof. F. V. Hunt's book "Electroacoustics" provided the solution to the theoretical design and a year later DuPont patented a new material called Mylar. All the previous main hurdles to a successful ES speaker had been overcome and several companies started to build prototypes.
By 1955, Peter Walker who owned Quad was demonstrating two prototype designs of ES speakers. One had an enclosure similar to the majority of all loudspeakers, and the other was an open back device. This second type was further developed to cover the whole audible frequency range and was first demonstrated as a working design in 1956.
The design of the ESL 57 remained virtually unchanged for its entire life in production. How many other products can this be applied to ? The ESL 57 was finally phased out after a production run of 25 years and 55,000 units produced.
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