Microphonics

microphonics [‚mī·krə′fän·iks]

(electronics)

Noise caused by mechanical vibration of the elements of an electron tube, component, or system. Also known as microphonism.

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Microphonics 

the phenomenon of undesirable changes in the parameters of an electric or magnetic circuit or of an electronic device that is caused by mechanical vibrations, shocks, and particularly by acoustic vibrations.

Microphonics produce interference during the operation of electronic apparatus, such as electrical audio-frequency amplifiers and superheterodyne radio receivers; they are heard as a characteristic ringing in the loudspeaker. In an amplifier they are caused mainly by movement of the electrodes in the input vacuum tube; in radio receivers, by the movement of the plates in the variable capacitor of the heterodyne circuit. The effect may be stimulated by a sound wave from a loudspeaker. It can be prevented by cushioning the tube sockets and the capacitor supports, by making the tube structure more rigid, or by avoiding the direct action of sound waves from a loudspeaker on the radio components. Microphonics are absent in semiconductor devices. The effect received its name because of the analogy between the physical processes in the effect and in a microphone.