Noise considerations in capacitative source microphones for telephone applications

The signal-to-noise performance of two types of piezoelectric ceramic microphones designed for telephone applications is compared with that of two electret microphones. It is shown that for the microphone sensitivities considered the noise produced by low-cost preamplifiers suitable for low-voltage operation in a telephone set is the limiting factor. While the electret microphone-preamplifier combinations are some 23 dB more sensitive, they are also some 21 dB noisier than the ceramic-preamplifier types considered so that the resulting signal-to-noise ratios for the telephone bandwidth (C-message weighting) are comparable.