Patent GB-918418-A (GB)
Title: Improvements in and relating to transducers
Inventor: HEINLEIN CARL TREVOR
IPC: H04R17/08
Filed: 1957-12-11
Abstract: 918,418. Gramophone pick-ups. COSMOCORD Ltd. Dec. 8, 1958 [Dec. 11, 1957], No. 38489/57. Class 40 (4). [Also in Group XL (b)] A piezo-electric element assembly, particularly for use as a transducer or gramophone pick-up, comprises at least two similarly shaped plates of the same piezo-electric material, e.g. monocrystalline material such as Rochelle salt, having similar surfaces thereof held together to restrain them against relative movement, one of the plates being of shear type and the other of extension type. In the construction shown in Fig. 7 the two plates 10, 20 are provided with electrodes 11, 12 and 21, 22, but a common electrode 12, 21 may be used on adjacent faces of the two plates. Clamping pads are applied along one edge as at 30 and at a diameter parallel to that edge as at 31. Force can be applied to a point along the parallel edge as at 32. A force at 32 tending to twist the assembly will produce an output on electrodes 11, 12 but not on 21, 22, whilst a bending force will produce an output on electrodes 21, 22 but not on 11, 12. A gramophone pick-up cartridge using the assembly of Fig. 7 is shown in Figs. 8 and 9 and is for use with a vertical and lateral or " hill and dale " recording system. The cartridge includes a composite transducer element 40 as described with reference to Fig. 7 which is connected by flexible leads 41, 42, 43 to output contacts 44. The element 40 is provided with a moistureproof coating, and is mounted in a casing 45 moulded from a synthetic resin and formed in one piece with an integral hinge portion 45a. The folded casing is secured by a rivet 46 to clamp the contacts 44. The element 40 is located in the casing by a rear pad 47 of plasticized polyvinyl chloride and an intermediate pad 48 of similar material. The pad 47 is located in the casing by projections 50 and the pad 48 by projections 52, the pad 48 presenting less compliance to bending than to torsional movement of the element 40. The front end of the element 40 is connected to a coupling member 53 by which motion is imparted to the element from a stylus 54 on an arm 55. The member 53 is made of a compliant material similar to that of the pads 47 and 48 and can be of various shapes to present different compressional and torsional compliances. Arm 55 is mounted in a grommet or plug 56 of material similar to that of pads 47 and 48. The stylus 54 is coupled to the member 53 either by small flanges on the arm 55 engaging the sides of the tip of member 53 or, as shown, by an extension on the end of the stylus at 57 which enters a hole in the member 53. The stylus 54 lies on the centre line of the assembly so that horizontal stylus movement wil produce a substantially pure torsional movement of the assembly. The member 53 can be formed with a projection 53a engaging the casing to help isolate the bending and twisting movements imparted to the element 40 and to reduce movement of the free end of the element 40. By a combination of the outputs of the two plates of the element 40, in appropriate phase, the cartridge can be used for a stereophonic or two-channel 45-45 degrees type system. Alternatively the construction shown in Fig. 10 can be used in which the assembly is rotated through 45 degrees about its longitudinal axis. The coupling member 53 is shaped so that the tip of the stylus 54 lies substantially on the centre line, at right angles to the plane of the element 40, thus passing through the torsional axis of the assembly so that a bending force only is applied to the element 40 by movement of the stylus in one of the two 45-degree directions.