GB322744A - Improvements in condenser telephones - Google Patents

Abstract

322,744. Vogt, H. Sept. 10, 1928. Loud-speakers; condenser telephones; diaphragms.-The diaphragm of a cordenser telephone is arranged between two stationary perforated plates and has a strong radial tension sucn that the restoring forees due to the deflection of the diaphragm increase with the attractive forces due to the charged capacity surfaces. The diaphragm 12, Fig. 6, has a tensile strength of from 20 to 40 kg. per sq. mm., a specific gravity of more than 3 and a thickness of 0.025 to 0.050 mm., and is more than 15 cms. in diameter. It is held between perforated plates 13 14, the gap between which is adjusted by insulating rings 15. The diaphragm is clamped between two metal rings 16, 17 by means of screws 18, Fig. 9, which deform the rings in the directions of the arrows and tension the diaphragm. These rings 16, 17 are attached to the capacity plates 13, 14 by screws 25 which also tension the diaphragm. Resilient washers 26 allow for temperature expansions of the diaphragm. The capacity surfaces are held together by screws 28, Fig. 5, with resilient washers 29 to allow for temperature expansions. The plates are constructed from a mouldable insulating material and the perforations are made by a casting process, an auxiliary layer 30, Fig. 10, being removed. They are then coated with an electrically conductive layer and further coated with a varnish of dielectric constant of above 3, such as acetyl cellulose, nitro cellulose, or a condensation product of formaldehyde and phenol. Sheets of cellulose film cover the capacity surfaces and prevent dust entering the air gap between them. The whole may be enclosed in a frame 66, Fig. 13, or casing which may also serve to house the necessary equipment.