Patent GB-275962-A (GB)
Title: Improvements in and relating to loud speakers
IPC: H04R19/00
Filed: 1927-07-27
Abstract: 275,962. Seibt, G., (trading as Seibt Fabrik Elekrischer Apparate, Dr. G.). Aug. 14, 1926, [Convention date]. Loud-speakers; condenser telephones and other electrostatic instruments; diaphragms. - An electrostatic loud-speaker is provided with a fixed electrode in the form of a polyhedron (cube or prism), the external surfaces of which are wholly or partly covered by the vibrating electrodes, or diaphragms. According to one construction, the loud-speaker is formed as a cube, diaphragms being fitted to its sides, the surfaces of which are perforated or grooved. Fig. 1 shows a further construction in which the core is formed as a brass cylinder having its exterior wall milled off so as to produce a polygon. The wall of the cylinder is either perforated or provided with grooves or channels. A diaphragm of indiarubber, celluloid or oiled paper, coated on one side with graphite, is placed round the prism so as to bear only on the edges thereof. If the external surface of the prism is insulated by coating it with varnish, a diaphragm of aluminium may be used or the conducting coating on the celluloid &c. diaphragm may be turned inwards. The diaphragm is preferably divided into a number of bands, as shown in Fig. 3, connected at their ends either with two small metallic pieces m, m screwed together or by means of a coil spring. Instead of using bands, silk threads which have been drawn through graphite of a colloidal consistency or thin copper or aluminiuim wires insulated with varnish or silk braiding may be wound on the varnished cylinder thread by thread. According to a modified construction of the form shown in Fig. 1, the core may be formed as an elongated prism of triangular cross section. The loud-speaker may be provided with an outer covering of artistic design. The Specification as open to inspection under Sect. 91 (3) (a) comprises also a construction Fig. 4 (Cancelled), in which two diaphragms M<1>, M<2> are each mounted on insulating rings r on two perforated metal members S, S connected together at a. The diaphragms may be of indiarubber or celluloid rendered conducting on the sides remote from the members S by a coating of graphite, or aluminium diaphragms may be employed, in which case, the surfaces of the members S are varnished or coated with perforated paper. In order to prevent contact of the diaphragms with the members S, the outer surfaces of the latter are preferably slightly curved. The loud-speaker when formed as a cube may have its internal core formed of solid metal containing numerous perforations, grooves or channels or of sheet-iron plates soldered together or of insulating material coated with graphite. The cube may be either suspended on a thread by one of its corners or secured to a foot. According to a further construction, a spherical loud-speaker is formed bv soldering together two hemispherical perforated sheet metal shells. The diaphragms consist of two hemispheres of celluloid, coated with graphite of a colloidal consistency, fitted over the metal core and stuck together with acetone. Small fragments of paper may be stuck to the surface of the core to ensure a uniform air gap. This subject-matter does not appear in the Specification as accepted.