GB270371A - Improvements in or relating to sound-reproducing apparatus - Google Patents

Abstract

270,371. British Thomson-Houston Co., Ltd., Young, A. P., and Hutt, J. Jan. 9, 1926. Magnetic instruments.-Relates to sound recording and reproducing apparatus, comprising a stylus-lever carrying a member such as an armature or coil movable in a magnetic field. According to the invention, in order that the styluslever may be aperiodic, it is mounted without any spring control and is restrained by damping- means. The stylus-lever may carry a coil adapted to generate or to receive currents corresponding to sound-waves, the lever being operated by a reproducing stylus, or actuating a recording stylus as the case may be. Fig. 1<a> shows a device for reproducing sound electrically from a gramophone record, comprising a pair of C- shaped magnets 11, having adjacent air-gaps 12. The main portions 13 of the magnets are preferable of cobalt steel, and the limbs 14 of soft iron. A pancake coil 15 is mounted on a stylus-lever 16, pivoted at 18, the coil lying in the air-gaps. The upper end 23 of the lever is located in a chamber 24, filled with damping material such as cotton-wool, a screw plug 25 being provided for adjusting the pressure of the packing. In a modification, the damping-device is similar to that above described, but the magnet is potshaped, and the coil is modified accordingly, to lie in an annular air-gap. Fig. 3 shows a further construction, also having a pot-shaped magnet 11, the upper end of the stylus-lever 16, adjacent to the coil 15, carrying a plate 31 located between two washers 32. The damping pressure between the washers and the plate 31 may be varied by adjusting two clamping-plates 33, 34 by means of screws (not shown). In another modification, Fig. 4, a ring magnet 11 in a non- magnetic casing 38 has pole-pieces 26, 27 connected to opposite faces of the magnet by magnetic strips 41, 39 respectively. A coil 15, carried by the stylus-lever 16, lies in the annular gap between the pole-pieces and damping is provided by strips of rubber &c. 42 mounted in slots in the inner pole-piece 27 and acting frictionally upon the former carrying the coil. Alternatively, the material 42 may be mounted in the outer pole-piece 26. In a gramophone embodying the invention, a sounding-board or baffle of the kind described in Specification 231,421 may be provided.