Electret condenser microphones.

For more than 4 decades electret microphones have dominated most transducer applications in the audio frequency range for three main reasons, linearity, simplicity, and they are inexpensive. E. C. Wente invented the condenser microphone in 1916 searching for a replacement for the carbon microphone used in most telephones, but it was impractical until the high-voltage battery was replaced with a permanently charged polymer. Electret microphones have been the workhorse for most microphone applications including microphones for professional sound level measurements, telephones, hearing aids, professional audio recordings, games, and toys. Recent worldwide estimates of the electret microphone market suggest that over 2 billion units are made annually. Electret condenser microphones are available in a variety of sizes from very small (a few millimeters in diameter) to about 2 in. in diameter. The use of multiple microphone elements in arrays and the use of digital signal processing provide interesting prospects for improving signal-to-noise. A variety of microphone arrays and some important historical facts will be discussed in this talk.