GB413819A - Improvements relating to moving coil loud speakers - Google Patents

Abstract

413,819. Loud-speakers. WILLSON, H. C., Walton, Bockminster Road, Wolverhampton. March 24, 1933, Nos. 8964 and 20985. [Class 40 (iv).] In a moving coil loud-speaker, the diaphragm is supported by a member disposed on the side of the diaphragm remote from the field magnet and does not depend for its support on a member on the same side of the diaphragm as the body of the magnet, the diaphragm supporting member engaging with the central core of the magnet or with a member attached thereto along axially directed surfaces formed respectively on the supporting member and on the central core or member attached thereto so as to ensure that the diaphragm and coil former are accuratelypositioned with respect to the field magnet. Fig. 1 shows a construction in which a cone 7 carrying a coil 8 has its outer edge 11 cemented to the rear of the rim 10 of a supporting member 6 having a central hub 5 into which a reduced projection 4 on the centre magnet core 1 is adapted to fit and be secured by a nut 12. A centring spider 16 is secured at 19 to the cone 7 and is clamped against the hub 5 by a washer 18 and nut 17. A cover 20 for the rear of the cone is bolted, riveted or cemented to the rim 10 and carries a transformer 21 or a terminal plate. The parts are assembled as follows. The cone 7 with the coil support 9 and spider 16 is placed on a cylindrical mandrel 23, Fig. 4, the middle portion of which is a sliding fit within the support 9. The mandrel is formed with a knurled portion 24, a central spigot 25 of similar length and diameter to the projection 4 and a projecting portion 26 adapted to be held in a chuck to allow the cone assembly to be rotated while the edge of the cone dips in a bath of adhesive. The diaphragm assembly still on the mandrel is then placed on the member 6, the spigot 25 passing into the hub 5 and a light cardboard ring 27 is placed on the edge of the diaphragm to prevent it sticking to a press in which the cone and its support are then placed. When the adhesive is dry the mandrel is withdrawn, the washer 18 and nut 17 are dropped within the former 9 over the threaded portion of hub 5 and the nut 17 tightened by the pin spanner shown in Fig. 5. This spanner has a handle 30, a body portion 28 fitting in the support 9 and provided with pins 31 which fit recesses in the nut 17 and a spigot 29 corresponding to spigot 25 and projection 4. The assembly is completed by fitting the cover 20 to rim 10 and securing the magnet by screw 12. Fig. 6 shows a modified construction in which a sheet metal member 6 is employed and the integral hub 5 is replaced by a composite hub consisting of bush 32 and nut 33. Shims 41 between the end of bush 32 and the abutting end 39 of the central core 40 ensure that the support 9 is accurately located axially with respect to the air gap. In this construction, the chassis or cover 43 is bolted to the magnet 2, an annular space being left between its outer cylindrical portion 44 and the rim 45 of the member 6, which space is filled with a felt ring 46.