GB1299124A - Electro-acoustic transducer - Google Patents

Abstract

1299124 Moving coil transducers PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 16 Jan 1970 [17 Jan 1969] 2197/70 Heading H4J A moving coil transducer, comprising pole plates 3 and 4, an annular permanent magnet 2, and a central core 5 forming part of plate 4, is such that it is assembled piece by piece in a sleeve housing 1 the inner surface of which is suitably shouldered on progressively larger diameters accurately, to locate the pole plates and ensure an annular gap between the core 5 and an aperture in the pole plate 3. The sleeve 1 is made of synthetic material. A diaphragm 8 can be fixed by adhesive to the pole plate 3 before assembly in the sleeve 1. If the diaphragm has a reinforced edge or an upturned locating rim it can be accommodated in the overhanging upper rim of the sleeve. A disc 15, located by adhesive, secures the assembly axially. The core 5 is hollow in register with a pad of damping material 20 in the securing disc 15. Instead of conforming to the circular edges of the pole plates the inner shouldered surfaces of the sleeve 1 may effect location by means of inwardly directed studs. Since it is desirable for the pole plate 4 to be of smaller diameter than magnet 2 the plate 4 may be located by a few radially directed lugs. The securing disc 15 may have an upwardly directed skirt 16, Fig. 4, and a tubular central portion 21 to enclose a back cavity and constitute a pressure transducer. The back cavity may be vented through matching apertures in the skirt 16 and side wall of the sleeve 1. To form a capsule for a telephone earpiece or mouthpiece, the sleeve 1 may be constituted by the inturned portion 31, Fig. 5, of a capsule casing 32. The bottom cover 35 provides the damped vent 21. While a securing disc fixed by adhesive is shown beneath the bottom pole plate, the assembly may be secured by deforming the depending edge of the sleeve 31 over the peripheral edge of the pole plate, Fig. 6, not shown.