GB447698A - Improvements in or relating to microphones - Google Patents

Abstract

447,698. Microphones. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, Westminster, and SUTTON, G. W., 25, Cranleigh Road, Merton Park, and GOODWIN, W. E., 72, Glyndon Road, Plumstead, both in, London. Feb. 7, 1935, No. 3973. [Class 40 (iv)] A differential telephone transmitter involving connections to three electrodes is constructed as one of the " capsule " type, i.e. the transmitter comprising the diaphragm, granule chamber, electrodes and other components is assembled as a unit ready for insertion into a holder provided with the necessary contacts for instantaneously completing the circuits through the electrodes. In the construction shown in Fig. 1, the microphone comprises a main casing 7 preferably of brass, separated from a metallic granule chamber 17 by insulating material 18, relative rotation of the parts being prevented by keys 19, 20 formed in the material 18 in assembly. One of the fixed electrodes 2 is carried by the inner brass wall 21 of the granule chamber, and the other fixed electrode 3 by a metallic sleeve 26 mounted in an insulating ring 24 that forms the outer wall of the granule chamber. The movable electrode 1 is secured to a rod 11 attached to the centre of the thin aluminium alloy diaphragm 4, the edge of which is clamped to the casing 7. A spring ring 33 serves to press the microphone against the mouthpiece part of the holder into which it is inserted, and with the casing 7 forms one of the three electrodes, the other two electrodes being constituted by the wall of the chamber 17 and by the spun over edge 27 of the sleeve 26, the annular form of all these electrodes permitting the contacts therewith to be unaffected by rotation of the transmitter in the holder. In a modification, Fig. 5, the main casing 45 is moulded from insulating material, and supports contact members 23, 46 and 49 connected respectively with the fixed and movable electrodes. In another construction, Fig. 10, a modulating member 67 of insulating material mounted on the rod 11 is adapted on movement to influence the distribution of granules between the electrodes 2, 3 and a third fixed electrode 66. Minor modifications are described in several further constructions.