ESL 57 Patents
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The patents listed in these menus do not, by any means, cover all patents ever granted in the area of electrostatic speakers. They concern the original Quad ESL in the main. Click the link above to see Quad ESL ‘63 patents. For example, I have deliberately left out significant work in the general field by Edelman (1930 - 31), and an ancient paper by Constantin Chilowsky and Paul Langevin [Sheet 1 , Sheet 2 ] (yes, the famous French physicist), in the area of electrostatics. The papers and patents referred to herein are those which are directly related to the development of the Quad electrostatic loudspeaker, as quoted by Walker and WIlliamson. Where possible, both the GB and US patents are referred to, assuming that they exist. Some US patents have no GB equivalent, and vice versa. If any reader of this page has knowledge of other interesting and directly related technical papers on this subject I would be glad to hear of these.
The Patents are arranged below in chronological order by date of grant, not date of application. This will settle the confusion in some people's minds as to why the speaker is sometimes referred to as the ESL55 and sometimes as the ESL57. These are the years of filing for U.S. Patents 3,008,013 and 3,008,014 respectively. The speaker should simply be called the Quad Electrostatic Loudspeaker, as the designers called it.