GB212648A - Improvements in sound emitting apparatus, such as telephone receivers - Google Patents

Abstract

212,648. British Thomson-Houston Co., Ltd., Butcher, J. H., and Young, A. P. Dec. 14, 1922. Magnetic instruments.-In sound transmitters or emitters, such as telephone receivers, the magnetic circuit and coil are arranged within a closed hollow casing 15 which functions as the diaphragm of the instrument, the moving element being connected to opposite sides of the casing. The casing 15 is preferably of boxwood, the magnets 17 being secured to the ends 14, which may be of aluminium. These ends 14 are carried on brackets 12 on a frame 11. The magnetic circuit may comprise two structures of soft iron laminations, each in the form of a rectangular C, with operating coils 18 mounted thereon. A permanently magnetized reed 22 is arranged in the air gaps and supported by rods 23 connecting it to the casing. The ends of the rods are screwthreaded and co-operate with nuts 25 for the purpose of adjustment. The reed may be pivoted at its centre. A longitudinal window of mica may be provided in the casing. The coils are wound so as to produce similar poles on the same side of the reed. The pole-pieces of the C-shaped magnets may themselves be permanent magnets of cobalt steel, or the main core may be a permanent magnet; in either case the actuating coils are disposed round the reed, which may be polarized or unpolarized. In another magnetic circuit, Fig. 3, the ends of permanent magnets 32 are connected by yokes 33 to pole-pieces 34, and a reed 22 is mounted between the pole-pieces in brackets 35 of non-magnetic material. Operating coils 18 are mounted around the reed so as to produce a consequent pole between the polepieces. In a further modification, in which the magnetic circuit and coils are associated with a closed hollow casing, the magnetic circuit, Fig. 4, comprises a number of curved magnets 36 arranged in the form of a circle, or a number of straight magnets in the form of a polygon. On one side of each magnet are fixed pole-pieces 37 to carry the actuating coils. A co-operating magnetic disc carried by the casing 15 is provided adjacent the faces of the pole-pieces. A similar structure may be used co-operating with a magnetic disc carried upon the other side of the casing 15. According to the first Provisional Specification, the reed which co-operates with two C-shaped magnet structures may be pivoted at its centre and connected at one end to a diaphragm or at both ends may be connected to diaphragms. With the arrangement shown in Fig. 3, the middle of the reed may be connected to a single diaphragm. According to the second Provisional Specification, a single bar-magnet, with L-shaped pole-pieces at each end on which are the actuating coils, may co-operate with a diaphragm clamped round its edge in brackets, and a number of curved or straight magnets in the form of a broken circle or polygon with polepieces adjacent their ends may co-operate with a diaphragm.