sound-powered telephone


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.