GB370188A - Improvements in or relating to microphones - Google Patents

Abstract

370,188. Microphones. MELODIUM S. A. R. L., 296, Rue Lecourbe, Paris. April 7, 1931, No. 10296. Convention date, April 7, 1930. [Class 40 (iv).] In a condenser microphone of the kind in which a conductive diaphragm is mounted in close proximity to a relatively fixed conductive surface, the fixed electrode is in the form of a thin conductive layer or coating upon a substantially perfectly flat ground surface of a glass or crystal block. As shown, the microphone comprises a conductive diaphragm 1 separated by a metallic ring 4 from the metallized surface 3 of a perfectly flat glass or crystal block 2 by a distance of the order of 0 .02 mm. The coating 3 may be applied by chemical deposition and the ring 4 may be deposited on the block 2 by a similar process, a line 5 made through the coating being sufficient to separate the ring from the remainder of the metallic surface. The block 2 may be perforated or provided with radial grooves 6 intersecting in a central aperture 7 so as to damp excessive vibrations of the diaphragm 1, the lead 8 to the electrode 3 being passed through the aperture 7. The parts 1, 2 are clamped together by metal rings 9, 9<1> and adjustable clamping screws 11 one of which may form the terminal for the lead 10 to the electrode 1. If desired, the diaphragm 1 may consist of a relatively thin glass or crystal plate coated on the side adjacent the block 2 in a similar manner to the block 2. The microphone may be connected in series with a battery, telephone receiver, amplifier and a high or low pass filter for selecting desired frequencies.