GB721325A - Improvements relating to electro-dynamic sound reproducers of the moving coil type - Google Patents

Abstract

721,325. Loud-speakers. WILLSON, H. C. June 30, 1953 [July 4, 1952], No. 16893/52. Class 40 (4). In a moving loud-speaker comprising separate readily detachable magnet and diaphragm units, an accurately machined aperture in the back wall of the diaphragm unit, with respect to which the moving coil M is accurately centred, serves by engaging the peripheral protruding cylindrical surface of the outer pole-piece C of the magnet unit when the two units are assembled to locate accurately the voice-coil in its working position by virtue of the prior centring of the inner pole-piece F with respect to an accurately machined and shouldered bore B in the magnet pot A into which the outer pole-piece is driven. The pot A is pressed and the front end bore is formed by cold extrusion. Spacing washers E may be of varying thickness according to the desired flux density. Jigs for centring the inner polepiece F with respect to the bore and the coil with respect to the chassis aperture are described with reference to Figs. 4 and 5 (not shown). The units are held together by a strap U which fits over the back of the magnet pot and is strained by a pair of opposite. threaded screws V. The strap U may also be used for holding the chassis to the coillocating jig. Alternative readily-detachable securing arrangements, one of which includes s spring clip, are described with reference to Figs. 5 and 6 (not shown). In a modification, the outer pole-piece is inserted wholly within the bore and a cylindrical centring or registering surface is formed by a shallow spigot on the front face of the pole-piece. Specification 660,800 is referred to.