GB348573A - Improvements relating to electrostatic loud-speakers - Google Patents

Abstract

348,573. Loud-speakers ; circuits for electrostatic instruments. RAUSER, A. and STEUER, W., 39, Kottbuser-Ufer, Berlin. Feb. 12, 1930, No. 4694. [Class 40 (iv).] In an electrostatic loud-speaker employing a diaphragm 10 which vibrates between perforated electrodes 4, 5 connected to the secondary 3 of the transformer supplying the speech alternating voltage, in order to avoid the use of an auxiliary source of direct current potential, a diaphragm is employed adapted to receive and hold a static charge. In the arrangement, Figs. 1 and 3, the diaphragm consists of one or more stretched layers of very fine films of resinous products, such as rubber, guttapercha, balata, amber, shellac, colophony, &c., either alone or in combination with an insulating supporting fabric of very fine texture and the diaphragm is charged, e.g. by rubbing, before insertion in the speaker. The films 10, Fig. 3, are either stretched directly on the electrodes or on frames 11, spacing strips 12 being located between the films and electrodes. According to the modification, Fig. 2, the diaphragm consists of two very fine fabric layers 13, 14, such as silk, between which is located a conducting or semi-conducting foil 15 which is connected directly or through a high ohmic resistance to earth or, as shown in dotted lines, to the negative pole of the anode circuit. It is stated that with such an arrangement the diaphragm automatically receives a static charge whenever the speaker is brought into operation, this charge being held during the operation of the speaker. The volume may be increased and the purity improved by connecting a high ohmic resistance 18 and also, if desired, a condenser 19 between the transformer windings 2, 3 as shown. Fig. 5 shows a constructional form of the loud-speaker employed in the arrangement shown in Fig. 2, each fixed electrode consisting cf a fine wire gauze 6 fixed on a coarse grating 7 and each silk layer 13, 14 being stretched on a frame 12, the foil 15 lying loosely between these layers. Specifications 1395/81 and 5870/82, [both in Class 40, Electric telegraphs &c.], are referred to.