GB248245A - Improvements in telephone receivers - Google Patents

Abstract

248,245. Western Electric Co., Ltd., (Bell Telephone Laboratories, Inc.). July 8, 1925. Telephones; diaphragms.-The diaphragm of a telephone receiver is heat treated to develop its maximum permeability at low magnetizing forces. Preferably, an alloy of nickel and iron is used, for example that described in Specification 188,688, [Class 82 (i), Metals. Extracting &c.], the finished diaphragms being heated to 1100‹ C. The diaphragms can thus be made of low mass for use on long subscriber loops where the magnetizing current and the flux densities in the diaphragm and pole pieces are low. In the receiver shown in Fig. 1, the diaphragm 10 and pole pieces 7 are produced as before stated, the winding 5 being on the centre leg of the E- shaped pole piece, the latter being welded to a mounting plate 8. In a modification, an additional perforated plate, produced as before stated, is mounted adjacent the diaphragm and serves as a magnetic shunt which becomes effective at higher magnetizing forces and minimizes acoustic shocks in the receiver. The diaphragm, on account of its low mass and high permeability, is particularly suitable for the receiver of a deaf set. illustrated in Fig. 9. The cap 30 of the receiver is embedded in an earpiece 25 moulded to the shape of the meatus of the ear and provided with a sound canal 35 which registers with the sound passage 21 of the cap 30.