piezoelectric microphone
A crystal microphone is a simple, piezoelectric microphone that uses the piezo effect to convert sound pressure into an electrical voltage. Hence the name piezo microphone.
In the crystal microphone, the speech diaphragm is firmly connected to the piezo ceramic, usually lead zirconate titanate(PZT). The sound pressure is therefore transmitted directly via the diaphragm to the piezo ceramic, where it is converted into an electrical voltage.
Crystal microphones have a very robust construction and were mainly used in the middle of the last century. They are not suitable for high quality audio recording. The characteristic sensitivity is about 10 mV related to a sound power( Pa) of 1 W/m2, which corresponds to a dB value of-60 dB. In comparison, moving coil microphones are -75 dB and ribbon microphones -80 dB. The frequency range of crystal microphones extends at about 10 kHz, and their impedance is high, between 2 MOhm and 5 MOhm. A disadvantage is also the high distortion factor, which is about 2%.