GB355227A - Improvements relating to the mounting of vibrating reeds, more particularly for use in connection with electromagnetic gramophone pick-ups, loud speakers and the like - Google Patents

Abstract

355,227. Sound recording and reproducing devices. WILSON, P., 48, Clarendon Road, Putney, London. May 15, 1930, No. 15018. [Class 40 (iv).] In electromagnetic sound recording and reproducing instruments, and particularly gramophone pick-ups, an armature is mounted so as to vibrate towards and away from one or more magnet poles so as to vary the length of the air gap between the armature and the poles, and a restoring force is set up as the armature vibrates, due to the magnetic action between the armature and two or more additional poles, which may, for example, be so placed that the vibrating armature sweeps past them so as to vary the overlapping area. In the construction shown in Figs. 1 and 2, and illustrated diagrammatically in Fig. 6, a U-shaped permanent magnet 1 has one limb in contact with an iron plate 2, which is fixed to a brass plate 3 abutting against the lower limb. The main poles 4 are screwed into the iron plate 2 and located in holes in the brass plate 3, and are surrounded by the speech coils 5. The additional poles 6 make contact with the lower limb of the magnet 1, and are fixed by screws 7 to the plate 3, their pole faces 8 being opposite lateral limbs 15 on an armature 9, which is pressed by a spring against steel balls, knife edges, &c. so as to vibrate about an axis x, Fig. 6, so as to move towards and away from the poles 4, the end faces of the lateral limbs 15 sweeping across the pole faces 8 to vary the overlapping area. The gaps between the pole faces 8 and the ends of the limbs 15 may be adjusted by turning the polepieces 6 about the screws 7. The main poles 4 may consist of tubes provided with plungers to increase the magnetic restoring force in the manner described in Specification 321,688, [Class 40 (iv), Telephones &c.], and mechanical damping- means, such as rubber pads, may also be employed. The armature may be made partly of magnetic and partly of non-magnetic material. In another form, Fig. 10 (not shown), one end of the armature vibrates between main poles 4 of opposite polarity, and the limbs 15 sweep across additional poles of opposite polarity. In the construction shown in Fig. 11, the armature 9 is of Y-shape, and its two limbs 30, 31 vibrate towards and away from poles N, N<1>, and across poles S, S<1>. A damping pad 32 of rubber &c. arranged between the limbs 30, 31 is adjusted by a screw 33. In other modifications, Figs. 12-14 (not shown), similar branched armatures are employed, in some cases with more than two limbs, and cooperating with poles differently arranged. Specification 349,146, [Group XXXVIII], also is referred to.