GB290558A - - Google Patents

Abstract

290,558. Electrical Research Products, Inc., (Assignees of Keller, A. C., and Norton, E. L.). May 14, 1927, [Convention date]. Magnetic instruments; phonographic recorders and reproducers.-A device for damping vibrations in acoustic apparatus comprises a pair of spaced relatively movable members mounted in a container filled with viscous material to such an extent as to maintain the opposing faces of the members covered, the material being moved laterally of the spaced members by the relative movement thereof. The invention is shown as applied to the armature of an electromagnetic - device for recording sound or for reproducing sound from a record. The armature 10 is held against a knife edge 14 by a spring 15 in the gap between the pole-pieces 12 of an electromagnet 10. Coils 17 surround the armature to which is attached a stylus holder 16 and stylus 19. The upper end of the stylus holder is connected by a rod 21 with a flexible diaphragm 24 clamped in a chamber 22 rigidly mounted with respect to the magnet 10, and filled with a viscous liquid 29, preferably a mixture of about 75 per cent polymerized castor-oil and 25 per cent nitro-benzol. In the centre of the chamber is mounted a post 23, the face of which is in close space relation to the diaphragm 24. In order to compensate for changes in the viscosity of the liquid prouced by changes in temperature, the post 23 is made of a material having a comparatively high linear expansion coefficient and the chamber 22 is constructed of a material having a comparatively low linear expansion coefficient. The length of the post is also made such that the changes in the length of the gap with temperature will be such as to compensate with the corresponding changes in the viscosity of the liquid. In the modified construction of damping unit, Fig. 5, a metallic plate 30 is mounted on the inner surface of the diaphragm. Specifications 290,264 and 221,283 are referred to.