Telephone Receiver


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telephone receiver

[′tel·ə‚fōn ri‚sē·vər]
(engineering acoustics)
The portion of a telephone set that converts the audio-frequency current variations of a telephone line into sound waves, by the motion of a diaphragm activated by a magnet whose field is varied by the electrical impulses that come over the telephone wire.

Telephone Receiver

 

the part of the telephone set that converts electric waves into sound waves. The telephone receiver and transmitter are both transducers and, with the exception of the direct-action granular-carbon transmitter, are in theory reversible. According to the principle governing the conversion of electric waves into sound waves, receivers are classed as electromagnetic, electrodynamic, or piezoelectric. As for construction, all modern telephone receivers are built as encased units, a design that ensures protection from moisture, ease of replacement, and stability of electroacoustic characteristics.

Figure 1. Design of a telephone receiver: (1) plastic casing, (2) outer cover with holes, (3) diaphragm, (4) pole pieces, (5) windings of the electromagnet, (6) coil form, (7) holes in the outer cover, (8) permanent magnet, and (9) plastic membrane

Electromagnetic telephone receivers are the most common. The main components of this receiver (Figure 1) are the permanent magnet (of hard magnetic material), magnetized pole pieces with windings of copper wire, and a diaphragm. The magnet is molded inside the casing of the receiver. The diaphragm lies over the casing and rather than being clamped is held in place in a stressed state by the forces of attraction from the pole pieces (both diaphragm and pole pieces being made of soft magnetic material). A membrane between the pole pieces and the diaphragm serves to control the receiver’s frequency response characteristic. The coil windings are connected in series, and the leads are connected to the terminals at the bottom of the receiver’s casing. When the alternating current of the telephone signal passes through the windings, changes are produced in the magnetic field that are reflected in the attractive forces acting on the diaphragm. The changing magnetic forces induce oscillations in the diaphragm, thereby reproducing sound.

Telephone receivers are used in telephone sets, telephone switchboards, and in such radio equipment as transmitter-receivers. They also find use in certain types of measuring bridges, where they are used as, for example, null indicators, and in audiometric devices, telephone headsets, and insert earphones.

Since the mid-1970’s, broad-band low-distortion electrodynamic telephone receivers have been used to control the quality of radio transmission and bring about the binaural reception of stereophonic transmission.

REFERENCE

Dubrovskii, E. P. Abonentskie ustroistva gorodskikh telefonnykh setei: Spravochnik, 2nd ed. Moscow, 1972.

L. I. KHACHIROV

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