GB435130A - Improvements in or relating to microphones - Google Patents

Abstract

435,130. Microphones. STANDARD TELEPHONES & CABLES, Ltd., 63, Aldwych, London.-(Assignees of Bennett, A. F. ; 900, Ridgewood Road, Millburn, and TUFFNELL, W. L.; 36, Coolidge Place, Hawthorne, both in New Jersey. U.S.A.) March 16, 1934, No. 8348. Convention date, May 11, 1933. [Class 40 (iv)] A microphone, more particularly for use in a telephone handset, comprises a movable domed electrode and a member or members forming a chamber adapted to receive granular carbon around said electrode, said member or members being shaped to form with said electrode a pair of reservoir chambers interconnected by a restricted passageway. As shown in Fig. 2, the microphone comprises a dished annular support 16 in an annular recess 18 in which the periphery of a frusto-conical diaphragm 19 located between paper leaves 20 is clamped together with an oiled silk screen 22 and a perforated protective cover 23 and washer 24 by a crimped band 25. The diaphragm, which may be provided with alternately long and short radial corrugations, has a central aperture in which is secured a dome-shaped member 26, preferably of gold-plated brass, which forms the front electrode. A silk closure member 30 and a metallic spider 32 are secured centrally at the junction of member 26 and the diaphragm and are clamped peripherally between an annular flange 33 on the support 16 and an insulating member 34, the arms of the spider forming an electrical connection between the electrode 26 and support 16. A fixed electrode comprising a domeshaped portion 35 and an annular flange 36 has the latter cemented to the member 34, this electrode and member 34 being secured to the support 16 by a clamping ring 38 threaded on to a tubular extension 17 of the support and bearing against a metallic ring 39 seated on an insulating washer 40 on the flange 36. A metallic cap 41 crimped over the edge of the portion 35 of the fixed electrode closes the filling aperture therein. The two electrodes 35, 26, the closure member 30 and the insulating member 34 form a chamber which is substantially filled with granulated carbon 42, such chamber, as shown more clearly in Fig. 5, comprising two relatively large reservoir chambers C and D which are connected by a restricted passageway E. Fig. 1 shows a handset having a microphone 12 constructed in accordance with the invention seated upon a shoulder in a dished member 13 threaded to a ring 14 which is in turn threaded to the handle 10, the microphone being retained in position by the mouthpiece 15 threaded on the member 13. Electrical connection between the electrodes 26, 35 and an external circuit is established by a pair of metallic springs 43, 44 mounted on the member 13 and insulated therefrom and from each other. The spring 43 engages the cap 41 and the spring 44 engages the clamping ring 38 which is electrically connected to electrode 26 through the support 16 and spider 32.