GB375010A - Improvements relating to sound reproducing instruments - Google Patents

Abstract

375,010. Loud-speakers. WILLSON, H. C., Walton, Beckminster Road, Wolverhampton. April 16, 1931, No. 11283. [Class 40 (iv).] A method of assembling the component parts of an electro-dynamic loud-speaker or the like involves the use of a jig, whereby the parts including the moving coil and its centring member are accurately positioned with respect to the magnetic air gap. During the assembling of the parts, the jig is temporarily mounted on the frame of the instrument, and after its removal the field magnet is fixed on the frame in a position coaxial with that previously occupied by the jig. The loud-speaker shown comprises a pressed steel casing a having a back-plate a<1> to which a permanent magnet b is secured, the magnet being enclosed by a dust cover c. The moving coil d<1> is carried by a tubular support d, attached to a conical diaphragm e, which may be made of moulded buckram &c., the diaphragm being peripherally secured to the frame a by rivets h. A flexible spider f, serving to centre the coil support and the attached inner end of the diaphragm, is carried by pillars g on a flat ring k, which is adjustably screwed to the plate a<1>. In assembling the instrument, the ring k is first loosely secured to the plate a<1> by screws passing through clearance holes. The tubular support d carrying the coil d<1> is next placed upon the projecting part m<1> of the jig m, Fig. 3, and the jig is fitted on to the back of the casing a, a shoulder m2 spigotting into an aperture in the back-plate a<1>. The jig is held loosely by screws passing into tapped holes in the ring k. A plug n is then inserted through the spider into a central hole in the jig, the head n<1> fitting accurately into the coil support d. The plug serves to shift the spider slightly, if necessary, to centralize it correctly. After the screws holding the rink k and the jig have been tightened up, cement is applied to the adjacent parts of the spider and coil holder d, and the projecting end e<2> of the diaphragm e is lightly pressed through the hole in the spider into the tube d. The rim of the diaphragm is then secured to the flanged edge a<2> of the casing by means of a clamping ring and rivets, and the jig is removed. Wires leading from the coil d<1> are soldered to connections on the spider, from which wires lead to insulated terminals on arms of the casing a. Finally, the magnet b is fitted with its shoulder b<1> entering the aperture in the plate a<1>, and is secured by bolts p, and the cover c is placed in position. Instead of positioning the jig and the magnet on the back-plate a<1> by means of shoulders entering an aperture, dowels or the like may be used.