GB420390A - Microphone - Google Patents

Abstract

420,390. Microphones. NEUMANN, G., 15, Michaelkirchstrasse, Berlin. July 17, 1933, No. 20193. Convention date, July 16, 1932. [Class 40 (iv)] In a microphone, more particularly a condenser microphone, having a thin, slightly stressed membrane, the restoring force of which is mainly determined by air cushions, the fixed electrode is provided both with closed bores of such a diameter and such a size that the air columns situated therein have a natural frequency above the audible range and also with bores which possess a greater volume than the first mentioned bores or are connected with separate air chambers and favour the lowest frequencies by resonance. The Figure shows a construction of condenser microphone in which a membrane 4 consisting of collodion film coated with beaten gold is pasted on the projecting edge 6 of the fixed electrode 5 in such a manner that the metal coating is not electrically connected with the edge 6. The electrode 5 is provided with closed bores 7 and also with a number of bores 7<1> which communicate with an annular chamber 10 closed by a cover 11, the sealing surface 12 of which is formed with a fine spiral groove which allows air to enter the chamber 10 along a long path but prevents all sound waves from passing to the interior of the chamber. The distances between the bores 7 may be varied and the bores 71 may be individually connected with an increased air space. An insulated contact pin 8 is connected with the membrane at 9.