The development of radio broadcasting about 1920 greatly stimulated electroacoustics. The carbon telephone transmitter was redesigned to use a stretched diaphragm and two buttons. E. C. Wente's condenser transmitter was applied to broadcasting. General Electric engineers developed a photoelectric microphone, called the Pallo‐photophone. Westinghouse engineers developed a cold‐cathode microphone using a direct‐current glow discharge in air about 1923. In Europe the Marconi‐Sykes magneto‐phone—a moving coil microphone—was used in England, and the Reisz carbon microphone in Germany and France. The ribbon microphone was proposed by Gerlach and Schottky in 1924. H. F. Olson was the first to realize the advantages of the directional response of the velocity ribbon microphone and developed a practical microphone about 1931. C. A. Hartman brought out a pressure‐actuated ribbon microphone in Germany in 1931. The directional pattern of the ribbon microphone has found wide application in motion picture recording and broadcasting especially since 1933 when J. Weinberger, H. F. Olson, and F. Massa designed a unidirectional ribbon microphone. The moving‐coil microphone was invented and patented by Siemens in 1877. The British Broadcasting Corporation in 1923 began using the Marconi‐Sykes magnetophone. In 1931 Bell Telephone Laboratories engineers announced a new type of high quality moving‐coil microphone which was improved in 1935 to have a nondirectional response. In 1919 Western Electric engineers under A. M. Nicolson made an extensive study of piezoelectric crystals. Some crystal microphones and phonograph pickups were used in English broadcasting in 1922 but the commercial application of piezoelectricity to acoustic devices was not made until 1930. By then, the Brush Development Laboratories had developed a cheap method of growing large crystals and cutting procedures as simple as wood‐working shop methods enabling them to make microphones, phonograph pickups, recording cutting heads, and loudspeakers.

This content is only available via PDF.