Patent GB-271125-A (GB)
Title: Improvements in and relating to telephonic receivers
IPC: H04R19/02
Filed: 1925-12-23
Abstract: 271,125. Graham, M., and Graham, A., (Representatives of Graham, E. A.), and Rickets, W. J. Dec. 23, 1925. Condenser telephones. - In an electrostatic telephone receiver in which one or more vibratile electrodes are arranged between fixed electrodes and charged relatively to the latter so that the electric forces set up are in equilibrium for the position of rest, the diaphragm is supported by flexible ties so that it may not be distorted. The electrodes may be flat or conical, and the vibratile electrodes may be attached to a suspended ring. The vibratile electrode 1, Fig. 2, vibrates between two fixed electrodes 2, 3, one or both of which may be perforated for the escape of sound; they may cornprise metal gauze screens each attached to a perforated sustaining grille 4. The perforations may be such as to produce a desired degree of air damping. The outer electrodes are oppositely charged by two sources of high voltage 5<a>, 6a, which are connected in series with inductances 9<a> and resistances 9, shunt condensers 9<b> being also provided. The vibratile electrode 1 is connected to the electrical mid-point of the system through the secondary coil 7 of the telephone transformer, a tapped battery 10 being provided if desired for purposes of adjustment. The input currents are applied to the primary coil 8. In modifications . the outer electrodes may be at the same normal potential and the source of current 5, Fig. 3<b>, (shunted or not by a condenser) may be located in the lead to the vibratile eectrode, the secondary coil 7 being then in one of the other leads as shown. The electrodes may be flat or, as shown in Fig. 3b, conical. The outer electrode may be constituted by the casing 4a of the receiver which carries the flare 4b. Alternatively there may be two vibratile electrodes 1, 1<a>, Fig. 4<a>, each being connected through a secondary 7 to one end of the source 5 and to the outer electrode from which it is furthest. A damping pad 3<a> may be provided. Or there may be three fixed electrodes 2, 3, 13, with two vibratile electrodes 1, 1<a>, between them; these may be either flat or, as shown in Fig. 6, conical. In this case the vibratile electrodes are at one mean potential, the fixed at another : the secondary 7 is connected to the central electrode. In the form shown in Fig. 7, the vibratile electrode is a rigid double cone 14, 15, whose vertices are spaced apart by a strut 20. The diaphragm is attached to a ring 16 which is suspended from fixed supports 19 by a series of radially arranged flexible but inextensible ligaments 17, 18, comprising thin wires or strong threads. Alternatively the cones 14, 15, may have their vertices inwards and bases outwards; or the ring 16 may carry a single flat electrode lying between flat fixed electrodes, or may carry two flat electrodes spaced apart by struts. In the form shown in Fig. 9, the conical electrode 1 is suspended by ligaments 17 and provided with a spider frame comprising a strut 25 and ties 21, the point 24 of the frame being connected to a further set of ligaments 22. Sanitary and hygienic devices.-In the form shown in Fig. 3<b>, the casing is earthed. In addition to preventing shock, this arrangement diminishes the deposition of dust.