GB188054A - Improvements in or relating to the vibratory diaphragms of sound-producing apparatus - Google Patents

Abstract

188,054. Marr, A. and Chalmers, A. M. July 29, 1921. Telephones. - Relates to sound-reproducing apparatus, such as telephone receivers and gramophone sound-boxes, of the kind in which, in conjunction with the ordinary or primary diaphragm there is provided a secondary diaphragm of smaller thickness adapted to receive its impulse from the primary diaphragm through an intermediate cushion of air. According to the invention, the thickness of the secondary diaphragm is not more than 50 per cent of the thickness of the primary diaphragm. As shown in Fig. 1, a secondary diaphragm 13 of aluminium, mica. or celluloid, is arranged above the usual iron diaphragm 11 of a telephone receiver after the iron diaphragm has been attracted by the electromagnet 12 whereby an air space 14 is left between the two diaphragms. The air space may alternatively be obtained by spacing the two diaphragms apart at their edges by means of a ring; and a packing ring may be interposed between the secondary diaphragm and the annular rib 15 of the cap 16. A small disc of aluminium may be attached to the centre of the inner side of the secondary diaphragm as a protection against accidental external pressure, when the disc will bear on the primary diaphragm which will resist the accidental pressure. An arrangement with a spacing ring 17 and packing rings 22, 23 is shown in Fig. 2 applied to a gramophone sound box in which tha secondary diaphragm 13 is recessed in the centre 26 to clear the connection 27 of the stylus arm 28 to the primary diaphragm 11. The edge of the secondary diaphragm 13 may be grooved to fit the spacing ring as shown in Fig. 3. The application of the invention to conical diaphragms carried by vibratory reeds is also mentioned.