Patent GB-263502-A (GB)
Title: Improvements in electro-magnetic apparatus for recording sound and record produced thereby
IPC: H04R9/12
Filed: 1925-06-22
Abstract: 263,502. Sykes, A. F. June 22, 1925. Addition to 210,956. Magnetic instruments.-Relates to detail improvements in sound-recording apparatus of the kind claimed in the parent Specification. According to the invention, '(1) in order to annual vibrations which would otherwise be set up in the magnet structure or the floating weight carrying the conducting recording strip and the associated parts, a compensating conductor adapted to produce electromagnetic effects substantially equal and opposite to those produced by the recording conductor is arranged adjacent thereto in the same or in a similar magnetic field; (2) the vibratory conductor is corrugated transversely, either wholly or partly, to obtain a wide range of amplitude of vibration; (3) the shape of the vibratory conductor is modified so that its ohmic resistance is greatest where there is the maximum amplitude of vibration, and. the shape of the field magnet poles may be shaped correspondingly. Fig. 1 (16094/25) shows a construction in which the conducting strip 1 carrying the stylus 3 is bent back on itself so that the upper portion 306 of the strip forms the compensating member, lying in the same field as the operative conductor. The open ends of the U-shaped strip are connected to insulated copper strips 107, 109, leading to the secondary 85 of a transformer which supplies the currents for vibrating the strip. The floating weight 65, to which the strips are bolted, carries an adjustable lever 83 having a springy portion 308 through which the strip 1 is looped. Oil, felt, &c., or a brush, is provided as damping-means acting upon the strip. The pivots of the floating weight may also be damped. The recording and compensating strips may be formed together as a coil 306, Fig. III (16094/25), one end of which is anchored at 312, the other end being secured to a slotted adjusting-lever 83. Figs. IV (Comp.) and V (Comp.) show a construction in which the vibratory recording element 1 is partly corrugated, and is set, together with the compensating member 306, between the magnet poles 9, 10. The primary winding of the transformer, of which the secondary is shown at 85, is supported by a bracket from the magnet structure. Other details are numbered as in the construction first described. In the modification shown in Fig. VI. (Comp.) the conductors 1, 306 are immersed in oil, vibration being transmitted through cords 320 or the like to a rocker 319 which carries the stylus 3. The above are examples of numerous alternative arrangements involving " compensating " conductor, which are described and shown. In Fig. I (21011/25) is shown a construction in which the styluscarrying conductor 1 is a corrugated strip stretched between a fixed conductor 107 and the compensating conductor 306. The return conductor 109 is insulated by mica from the part 107, and both these conductors are soldered to the ends of the secondary winding 85 of a transformer. A damping medium 318, such as petroleum jelly, is inserted between the parts 1, 306. The primary winding and the core of the transformer are shown at 141, 88 respectively. The secondary is formed of a spiral copper strip, the space between the convolutions being bounded by shellac, and the whole forming a floating beam pivoted at 66 on a spindle sleeved with rubber. The field magnet is surrounded by a magnetic shield. A modification of the apparatus is described, adapted to produce lateralcut records. Figs. I. (10645/26) and II. (10645/26) show alternative forms of apparatus in which the conductor 1 is reduced in width and/or depth at its central portion, the magnet pole-pieces 9, 10 being shaped correspondingly. Further concentration of the magnetic field may be attained by using special alloys, such as nickel iron, for the polar extensions. Fig. VIII. (Comp.) shows an arrangement in which the field magnet itself constitutes the input transformer, current being induced in the secondary circuit 85 by the changes in the field magnet current. The entire magnetizing current may be the anode current of the valve 46; or it may be supplied by the battery connected as shown, suitable chokes being provided. Fig. II. (Comp.) shows a method of mechanical damping, in which a cord 400 is threaded through the stylus attachment 401. The other end of the cord is attached to a loose coil or distant support. The cord, which may be twisted cable with a fluffy covering, absorbs energy in the form of a ripple. Fig. I. (Comp.) shows the general arrangement of a recording-apparatus embodying the invention. The field-magnet is clamped between a member 314 and a housing 114 for supporting the transformer core 88. which may be gapped, for preventing saturation. The member 314 is pivoted at 384 on a vertical support 385, itself pivotally supported in bearings 387. A screw adjusting device 390 engaging with a ball-and-socket joint 391 permits the magnet structure to be raised or lowered relatively to the blank 4. A shield 338 protects the phonograph mechanism from magnetic effects. Specifications 224,936 and 258,137 are referred to.