Patent GB-384315-A (GB)
Title: Improvements in means for converting electrical vibrations into sound
IPC: H04R11/00
Filed: 1931-05-26
Abstract: 384,315. Loud-speakers, pick-ups, &c. LEWIS, J. H. W., 31A, Farm Lane, Fulham, London. May 26, 1931, Nos. 15442 and 17937. [Class 40 (iv).] Relates to devices for interconverting electrical and acoustic vibrations, such as loud speakers or gramophone pick-ups, of the kind having an L-shaped reed vibratable in a constant magnetic field. According to the invention, one end of the reed is attached to the permanent magnet by wedging or clamping it between the magnet and an auxiliary clamping or wedging member. The loud-speaker unit shown in Figs. 3 and 4 comprises a cast aluminium baseplate 20 having an upstanding rectangular wall 22. Within the wall, as in a box, a rectangular permanent magnet 23, a laminated polepiece 25, and an L-shaped reed 24 are secured, the reed being held between the wall 22 and one end of the magnet, and the polepiece (which, together with an attachment 25a is T-shaped) being similarly secured at the other end. The wall is deformed at 27, to wedge the parts tightly in position. The upper portion of the reed 24 tapers towards the free end, which lies between the end of the polepiece 25 and a magnetic stirrup 30. This is fixed by having its ends wedged between the member 25a and the side parts of the wall 22. A rod 28 connects the reed to a diaphragm. Adjustment of the reed is effected by a screw 32, bearing against a spring 31 fixed to the reed. A coil 26 surrounds the polepiece 25, and is connected to terminals 34 which project through an aperture in a removable cover (not shown). Fig. 5 shows a modification, in which the reed 24 and the polepiece 25 are secured on the inside of the rectangular magnet 23 by being wedged between the magnet and an internal member 36. As an additional securing means, the reed and pole piece may be screwed to the part 36. Modifications similar to that shown in Fig. 5 are described, in which the end portions of the reed and polepiece that engage the magnet are bent round it, the extreme ends of these parts being either on the inside or the outside of the rectangular magnet. The single magnet may be replaced by two parallel bar magnets spaced apart by distance-pieces, around which the reed and polepiece are bent. Further constructions, Figs. 8-11 (not shown), which are similar to that shown in Figs. 3 and 4, are described, but in these cases instead of holding the magnet system in a box-like structure the parts are clamped together by means of lugs bent up from a sheet-metal baseplate or formed integrally with a baseplate of substantial thickness. In Fig. 13, the reed and polepiece are shown as being held in position by the clamping action of screws 42, passing through a rectangular ring 122 which surrounds the magnet system. An arrangement employing parallel bar magnets 123 and distance-pieces 44 is shown in Fig. 14, packing pieces 45 being provided on either side of the polepiece 25. The whole magnet system is gripped between ears 38, which are bent. up from the base 20. Still another modification is shown in Fig. 15, in which an end of the reed 24 lies in contact with an outer face of the rectangular magnet 23, and has a central tongue 46 bent out and embracing the end member of the magnet. A clamping or wedging member (not shown) is also provided.