CRYSTAL MICROPHONES
Certain crystals, such as rochelle salt and quartz possess the property of generating small emf's when subject to stress or strain. This effect is utilised in what is known as the crystal microphone.
The construction of a crystal microphone is shown in Fig. 2.8. A thin finger shaped slice of crystal is secured at one end by means of a compliant clamp, and the apex of a cone is made to bear against the other. Sound pressure waves cause the cone to alternately press against and bend the crystal slice and release it. Thus, corresponding voltages are generated across the slice. A pair of contacts is fixed to opposite surfaces to take off the signal.
Fig. 2.8 Simple crystal transducer: (a) Crystal slice is secured at one ...
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