GB294147A - Improvements in and relating to apparatus for the interconversion of mechanical and electrical oscillations, such as loud-speakers - Google Patents

Abstract

294,147. British Thomson-Houston Co., Ltd., (Assignees of Guedon, E. C.). July 18, 1927, [Convention date]. Magnetic instruments.-A device for converting electrical impulses into sound or vice versa comprises an armature in the form of a hollow member of oval cross-section having a slot along one of its wider sides formed by folding over a piece of sheet metal so that its opposite edges nearly meet. The armature is preferably so mounted that it rotates about an axis near its centre of mass. In the construction of loud-speaker shown in Fig. 1, the electromagnetic unit is clamped by bolts 2 to a support 1 and is coupled to a conical diaphragm 3 through a rod 4. The unit comprises a magnet 5 provided with U-shaped polepieces 6, 7, Fig. 3, adapted to support a coil 8. An armature 11 is pivoted within this coil and is connected to the rod 4 through a rod 12 and a resilient member 13 attached by a screw 14 to the pole-piece 7. The armature 11, Fig. 5, is made by folding a sheet of metal so that its opposed edges are slightly spaced apart, punchedout portions 15, 16 forming pivotal lugs which are fixed in slots 19 in the member 18 forming part of the spool on which the coil 8 is wound. The pole-pieces 6 ,7 are attached to the magnet 5 by screws 16', Fig. 3, which preferably extend through slots in the ends of the magnets so as to permit of adjustment of the air gap between the pole-pieces. Fig. 7 shows a modified form of armature 21 in which the lugs 15, 16 are replaced by a resilient bar 20, which is either pivoted in the coil spool as previously described or attached to a non-magnetic collar 22, Fig. 9, which is spun over the inner edges of the spool. In this latter modification, the driver rod 23 has one end fitted into the slot in the armature, its other end being threaded for attachment to a diaphragm or to a stylus holder. In a further modification, Fig. 12, the armature 24 is supported by a pair of resilient members 25 fixed either to the collar 22 or to the coil spool. Specification 249,603 is referred to. The Specification as open to inspection under Sect. 91 (3) (a) comprises also a further modified form of armature, Fig. 13 (Cancelled), made by folding a T-shaped sheet so that the top of the T forms lugs 26, 27. This subject-matter does not appear in the Specification as accepted.