GB191310399A - Improvements in Telephones. - Google Patents

Abstract

10,399. Plecher, A. May 2. Microphones. - In a microphone without granules one electrode is made of rubber or the like and bears a film of gold-leaf, or of silverleaf, platinum, aluminium paint, graphite, or other conducting material. The electrodes have parallel extended surfaces, one of which is scored or checquered so as to present numerous points to the conducting films 33 on the other: hence microphonic and electrostatic action are combined. The membrane 32 is engaged between two clamping- rings 34, 35, which are separated by ball bearings 37 from the cap 30, by screwing which the natural frequency of the diaphragm can be adjusted to the average of that of the sounds received. The membrane 32 bears a conducting film 33 facing the numerous points 40 on the insulated electrode 14a which is resiliently mounted between springs 43, 45, and may be of carbon, of gold- or silverplated copper, or of metal-coated rubber. When at rest the film 33 is out of contact with the electrode, and when in motion it sets up microphonic and electrostatic action alternately. Several such microphones may communicate with a single mouthpiece. They may also be used as electrostatic receivers or circuit-closers, particularly in connexion with wireless telegraphy.