GB1262505A - Speaker system and electrostatic speaker - Google Patents

Abstract

1,262,505. Electrostatic speakers. L. J. BOBB, and C. C. POND. 25 April, 1969 [29 April, 1968], No. 21291/69. Heading H4J. An electrostatic loud-speaker comprises two spaced parallel, perforated substantially planar electrodes (preferably divided into five sections 12) and a pair of spaced, parallel, substantially planar, coextensive membranes 8 disposed between the electrodes and acoustically coupled together by air in between. In operation the combination of a conductive coating on one membrane 8 and the adjacent perforated electrode is electrically in push-pull with the combination of a conductive coating on the other membrane 8 and electrode. The two membranes 8 of polyester are coated with aluminium on their confronting faces and are clamped together between two frames 5 which press their coatings into contact with perforated aluminium strips 9. The membranes 8 are omni-directionally stretched and the perforations in the strips 9 prevent slipping. The frames 5 have mullions 16 which define twenty-five windows. Each set of five perforated metal strips 12 is sandwiched between damping gaskets 14, 15, also windowed, and there is a peripheral gasket 11 of blotting paper between each gasket 15 and membrane 8. Additional damping material 17 is provided in at least the peripheral windows. The air space between the membranes 8 is air vented by a gap 10 between adjacent strips 9. The perforated electrodes are connected to opposite ends of the secondary winding 18S (Fig. 4) of a transformer. The conductive coatings on the membranes are connected to the centre tap through a polarizing voltage source Ep and a resistor 20 which keeps the polarizing voltage charge substantially constant. Connection to the conductive coatings is through a tab 9a on one of the strips 9. The outermost pairs of sections 12 are connected through resistors 24, 25 which attenuate intermediate and higher frequencies, the intermediate pairs of sections 12 are connected through resistors 24 which attenuate intermediate frequencies and the innermost sections 12 are connected without frequency attenuation.