In 1877, Werner von Siemens invented the electronic acoustic transducer based on the electrodynamic principle-according to the principle of the plunger coil generally applied today. Initially the transducer was used as a telephone receiver. With the appearance of power amplifiers around 1920, the Siemens laboratories began to manufacture a number of different designs, which eventually gave rise to the loudspeaker combination Euronor of Klangfilm GmbH in 1937. Other trend-setting loudspeakers by Berlin inventors worthy of mention include the electroacoustic Statophon by Hans Vogt, dating from 1921 and the O 15 with coaxial bass and treble chassis, by Hans Eckmiller, used at RRG Studios from 1943 onward.
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