Basic Operating Principles of Microphones

  • John M. Eargle


The use of microphones began with the telephone in the last quarter of the nineteenth century. The requirements were basically those of speech intelligibility, and the carbon microphone, developed early in that art, is still used in telephones today. The carbon microphone works on the loose-contact principle, as first demonstrated by Emile Berliner. Particles of carbon are alternately compressed and relaxed by the diaphragm under the influence of sound pressure, and the resulting alternation of resistance modulates the current proportional to the change in resistance. Carbon microphones are noisy, have limited dynamic range, and produce high levels of distortion. None of these defects is really serious in their application to telephony, however.


Sound Pressure Fixed Charge Speech Intelligibility Polarize Voltage Capacitor Element 
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Copyright information

© Chapman & Hall, New York, NY 1996

Authors and Affiliations

  • John M. Eargle

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