The electret technology has been applied to the design of subminiature condenser microphones in an unusual manner. The use of a nontensioned disphragm and the separation of diaphragm and electret functions permit the charge storage function, the frequency response, and the temperature coefficient to be independently optimized. The resulting microphones are characterized by an unusually low vibration sensitivity, noise level, and temperature coefficient, combined with a high degree of reliability. The range of selectable parameters permits the ready attainment of flat extended range devices for research purposes or tailored frequency response devices for use in hearing aids.
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