GB791335A - Improvements in and relating to electric circuits for use in sound reproduction - Google Patents

Abstract

791,335. Circuits for electrostatic instruments. FERGUSON RADIO CORPORATION, Ltd. May 13, 1955 [May 13, 1954], No. 14094/54. Class 40 (4). A circuit 20 for an electrostatic loud-speaker comprises a thermionic valve 10 operating as a constant current device, and having in its anodecathode circuit a tuned circuit comprising an inductance 12 and the electrostatic loud-speaker 16 one terminal of which is connected to a condenser 17 for blocking the application of H.T. thereto, a suitable polarizing potential being connected to said terminal over resistance 18. As shown, Fig. 1, two such speakers 15, 16 operative over different frequency ranges are used in the circuit 20. Further pairs of speakers covering other frequency ranges may be connected in series as shown at 20<SP>1</SP>. Fig. 2 illustrates an alternative embodiment wherein separate blocking condensers 17, 17<SP>1</SP> are used for the speakers 16, 15. If a three-element loudspeaker is used, then the loud-speaker 16 may represent one fixed plate and the diaphragm and the condenser 17 the other fixed plate and the diaphragm. In this case the inductance 12 is centre tapped and one half of the coil only is included in the anode-cathode circuit. Push-pull voltages for the two halves of the loud-speaker are thus obtained by autotransformer action. The circuit of Fig. 2 may also be modified by providing further coils tightly coupled to coils 11 and 12 and included in the anode-cathode path of a second valve, the two valves being driven in push-pull.