The carbon microphone used in telephone mouthpieces has thin diaphragm behind which are packed tiny carbon granules. Sound waves vibrate the diaphragm, exerting a variable pressure on the granules. This varies their electrical resistance, so producing fluctuations in a DC current passing through them.
The crystal microphone incorporates a piezoelectric crystal in which pressure changes from the diaphragm produce an alternating voltage.
In the electrostatic microphone the diaphragm acts as one plate of a capacitor, vibration producing changes in capacitance.
In the moving-coil microphone the diaphragm is attached to a coil located between the poles of a permanent magnet; movement induces a varying current in the coil.
The ribbon microphone has, rather than a diaphragm, a metal ribbon held in a magnetic field; vibration of the ribbon induces an electric current in it.
Related entry hydrophone
Related categories ACOUSTICS AND MUSIC
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