GB1334347A - Electrostatic transducer - Google Patents

Abstract

1334347 Electrostatic transducers; earphones STANTON MAGNETICS Inc 12 June 1972 [19 Aug 1971] 27387/72 Heading H4J An electrostatic transducer comprises a diaphragm 36 (Fig. 3) secured to one face of a frame 24 having a central opening 26. A perforated plate 28 of conductive material coated with insulation is secured to the other face of the frame 24. Spacers 54, of foam rubber or foam plastics material having a foam rubber-like resilience, in the form of discrete clumps near the sides of the frame 24 (preferably near the corners) project into the opening 26. Electrical connections are provided to the diaphragm 36 and to the plate 28. The diaphragm 36 is preferably of polyethylene terephalate film having a vacuum deposited metal coating 38. The transducer is preferably of the push-pull type having a second plastics film 46 overlying the metal coating 38, a second frame 48 and a second perforated plate 50 provided with foam spacers 54 (see Fig. 4) in register with the first spacers 54 for uniformly supporting diaphragm 36 and film 46. The transducer may be used in a loudspeaker or earphones. The frames 24, 48 are formed from epoxy resin or glass fibre reinforced polyester film. The plates 28, 50 are of metal, coated with varnish or, preferably, are anodized. The diaphragm 36 is adhered to the frame 24 and is neither limp nor tightly stretched. Film 46 is similarly adhered to frame 48. Registering holes 52 receive screws or clips Earphones 10 (Fig. 1) comprise an adjustable strap 12 and earpieces 14. Each earpiece 14 includes a housing 16 in the form of a concave shell provided with a cushion 18. A transducer (20), Fig. 2 (not shown), within each housing 16 had leads fed through a universal joint 22 which also connects earpiece 14 to strap 12. The earphones are for stereophonic use. Local circuit.-Each earphone transducer is fed by a step-up transformer 56 (Fig. 5) having a secondary winding 58, the ends of which are connected to the plates 28 and 50. A centre tap 60 is fed through a polarizing voltage supply 62 to metal coating 38. The plate 28, which in use is close to the user's ear, is earthed.