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maritime DC & PPE Information Center


Sound-Powered Telephone System


Sound-powered telephones are telephones powered by the sound pressure of your voice rather than batteries or an electrical power source. Phones work properly by speaking in a strong, clear voice, which generates enough current to carry your voice to all other phones on the circuit. When you speak into the mouthpiece, the sound waves of your voice cause a diaphragm to vibrate. The vibrations are transferred from the diaphragm through a drive rod to an armature centered in a wire coil. The current then is transmitted to a receiver (the earpiece), where the process is reversed. The person at the other end of the circuit hears the sounds transmitted.

The earpiece, though shaped differently from the mouthpiece, also contains a diaphragm, an armature, and a coil. The earpiece and the mouthpiece can be used interchangeably; you can talk into the earpiece or hear through the mouthpiece. This feature is important to remember should a failure occur in one of the pieces. It is also important because you need to be aware that an earpiece turned away from your head will pick up distracting noises.


Image of Sailor using sound-powered telephone

For more information, see the Index.