GB598753A - Improvements in microphones - Google Patents

Abstract

598,753. Microphones. DEAR, A. E. Sept. 8, 1945, No. 23175. [Class 40 (iv)] A carbon granule microphone has a single fixed electrode co-operating with two vibrating electrodes, the granule chamber being defned by the fixed electrode and a convex surface of each vibrating electrode. The fixed electrode is contained in an insulating case inside and coaxial with a metal case to which the peripheries of the vibrating electrodes are attached. The fixed electrode F, Fig. 3, has a conical recess formed in each face, whose angles correspond to that of a similar depression in each metal diaphragm G. The electrode F is also pierced by a number of radial slots and carbon granules R are packed between the central electrode F and the two diaphragms G, being retained at the periphery by flexible insulating washers E. The central electrode is held in an insulating casing C inside a metal casing A closed by a cover B. which also clamps the whole assembly together and holds perforated grilles K, L and spacers D, H, J in position. A stud N insulated from the metal casing by a collar M is screwed into the central electrode as an electrical connection. When it is removed, the hole communicates with one of the radial slots in electrode F and it is used for filling the chambers with granules. A stud screwed into the metal casing A serves as the second electrode.