Patent GB-320910-A (GB)
Title: Improvements in sound records and recording machines
IPC: G11B3/00
Filed: 1928-04-19
Abstract: 320,910. Columbia Graphophone Co., Ltd., and Mitchell, F. A. April 19, 1928. Feed - mechanism ;speed-regulating ; soundgrooves. -Relates to sound-recording machines in which the radial feed of the recording stylus is varied to accommodate different amplitudes of the sound waves being recorded, the rate of feed being increased for sounds of large amplitude, and consists in providing a dashpot or the equivalent to maintain the increased pitch distance for at least one turn immediately after a large amplitude sound wave has been recorded. Fig. 3 shows a manually-controlled machine in which the turntable T is rotated through gears K, K<1> from a motor-driven spindle S, and is traversed under the recording stylus N by mounting it on a carriage F, moved along a frame Q by the action of a feed screw S<1>. The screw is driven by the spindle S through variable friction gear L, L<1> L<2>. The position of the intermediate wheel L<1> is adjustable by means of a hand-lever J. Normally, the lever J is set to the position indicated by the word " Quiet," but when the operator knows that sounds of large amplitude, are to be recorded, he sets the pointer to the indicator " Loud." This increases the speed of travel of the turntable. A dashpot slow-return device is attached to the lever J, to provide a sufficient delay before, the pitch distance is reduced after the large amplitude sounds have ceased. Rack, lever, or other suitable mechanism may be substituted for the screw spindle S<1>. The machine shown in Fig. 4 is designed for producing records of the " constant linear velocity " type. Two motors are provided, one M for traversing the turntable T beneath the recording stylus N<1>, whilst the motor M<1> rotates the turntable T through a friction disc L<3> at the necessary varying angular speed. Governors O, O<1> control the speed of the motors, and by means of a lever O<3> acting on the governor O the operator varies the rate. of feed of the turntable as necessary. A dashpot slow-return device may be attached to the lever O<3>, to maintain the increased pitch distance for the required period after large -amplitude, sounds have been recorded, or preferably the mechanism shown in Fig. 5, is employed. This comprises. a wheel or disc H<3> driven uniformly by the shaft S<3>, and carrying on its side a friction disc H<2> adapted to engage a contact member H in such a manner that normally the end H<1> is pressed against a fixed contact V. When large-amplitude sounds are to be recorded, a magnet U is energized and attracts the contact-piece H<1> to the position shown in dotted lines. This causes a magnet V<2>, Fig. 4, to be energized and shifts the lever O<3> so as to increase the rate of feed of the turntable. The circuit of the magnet U is broken when the sounds of large amplitude have ceased, and the contact piece H<1> is gradually returned by the rotating disc H<3> to its normal position. The circuit, through the magnet V<2> is maintained until the member H' reaches the contact V, but is broken when this occurs, whereupon the lever O<3> is returned by a spring to the " Quiet " position. The machine shown in Fig. 4 may be modified by providing means for gradually varying the relative positions of the friction disc L<3> and the stylus N', so that a record which is recorded neither at constant angular nor constant linear speed may be produced. Hill-and-dale recording, instead of lateral-cut, may be effected. The recording stylus may be biased, either by an amplifier or mechanically, so that the sinuosities of the sound-groove mainly lie on one side, as shown diagrammatically in Fig. 8. The Specification also describes the application of the invention to apparatus or systems which are described in Specification 321,153, and which comprise (a) a machine in which the variations of pitch distance are controlled automatically in accordance with the amplitudes of the sound being recorded, and (b) a system of recording in which two electric pickups are used in conjunction with a single master record or with two similar master records working together, to produce another record in which the pitch distance is automatically controlled.