GB218743A - Improvements in telephone receivers, loud speaking telephones, and the like sound emitting devices - Google Patents

Abstract

218,743. British Thomson-Houston Co., Ltd., and Young, A. P. April 11. 1923. Magnetic instruments.-A sound transmitter or emitter, such as a telephone receiver, comprises a hemispherical vessel of magnetic material 11 with a permanent bar magnet 12 located axially therein and a vibratory member of magnetic material mounted with its edge adjacent to the edge of the vessel. The coil 16 may be mounted around a portion of the permanent magnet, which may be reduced in section and may be of round or square cross-section. The vessel may form the external casing of the instrument, and may be bronzed or lacquered. The vibratory member may be a diaphragm 13, Fig. 1, or may be mounted upon a sounding board of wood, cellulose acetate, mica, paper or other materials. Two vessels 11, Fig. 2, may be secured together with overlapping flanges and made sufficiently resilient at their rims to act as vibratory members. A permanent magnet 12 may be secured centrally of each vessel with an air gap between the adjacent poles, and an operating coil 16 may be mounted on brackets, or may be split in two with portions on the free ends of the magnets connected by a resilient conductor. A single magnet may be carried axially of the casing on brackets, and a coil mounted on each end adjacent the interiors of the two hemispherical vessels. The hemispherical vessel may be hung, Fig. 1, so that the diaphragm is horizontal. According to the Provisional Specification, the permanent magnet may be secured in the casing by means of a screw or by moulding it in position with the aid of an insulating material such as synthetic resin, and the casing may be coated with moulded insulating material or mounted in a casing made of such material. A straight bar permanent magnet may be mounted between two vibratory iron diaphragms which may form the ends of an iron cylinder, or two bar magnets may be used secured at their outer ends to the casing. A single hemispherical bowl may be suspended with the diaphragm above or below the bowl. Specifications 1912/98 and 600/12 are referred to.