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Home Electroacoustic Devices The Magnetic 'Sound-Powered' Telephone Transmitter
 
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The Magnetic "Sound-Powered" Telephone Transmitter

The sound-powered transmitter is of the generator type. Acoustic power from the sound waves is converted into electric power; hence the wording "sound-powered." As explained in the section on Passive or Generator-Type Telephone Transmitters, the electric power output is very low, and such transmitters are used only in special telephone systems where the talking distances are small and the transmission losses are low.

A schematic diagram of a sound-powered magnetic telephone is shown in Fig. 6. Sound waves striking the diaphragm cause it to move, and this motion is imparted to the small soft-iron armature which conducts magnetic lines of force between the soft-iron pole pieces. As this armature moves in accordance with the speech sounds, the magnetic lines of force linking the coil are caused to vary, and this induces in the coil an electromotive force that is a good replica of the sound waves. This transmitter can be used also as a telephone receiver.

Figure 6. Schematic diaphragm of a sound-powered telephone transmitter. The internal impedance is 900 ohms at 1000 cycles. For very loud talking the generated voltage is about 50 millivolts. This device may also be used as a receiver. (Courtesy Automatic Electric Co.)


Home Electroacoustic Devices The Magnetic 'Sound-Powered' Telephone Transmitter

Last Update: 2011-05-30