sound-powered telephone


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sound-powered telephone

[′sau̇nd ¦pau̇·ərd ′tel·ə‚fōn]
(engineering acoustics)
A telephone operating entirely on current generated by the speaker's voice, with no external power supply; sound waves cause a diaphragm to move a coil back and forth between the poles of a powerful but small permanent magnet, generating the required audio-frequency voltage in the coil.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.