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Consumer Electronics by S. P. Bali

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ELECTRET MICROPHONES

In electret microphones, Fig. 2.15, a permanent electrostatic charge is implanted into the metallised diaphragm, thereby eliminating the need of an external high-voltage source.

 

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Fig. 2.15 (a) Construction details of electret microphone (b) Sony 6.38 B studio microphone

 

One way of doing this is to put the diaphragm sheet between the plates of an air-spaced capacitor which is then charged upto a high voltage. The sheet is then heated and allowed to cool with the charge still maintained across it. When it is removed, it has a permanent static charge which is the equivalent of an applied voltage of around 100 V. This ...

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