GB322033A - Improvements in or relating to the recording and reproduction of sound - Google Patents

Abstract

322,033. Brown, S. G. Sept. 21, 1928. Records ; magnetic apparatus.-A sound record is formed by guiding an electromagnet A immediately over a ridge b<1> in the form of a spiral or other uninterrupted path provided on the surface of an unmagnetized blank B of permanently magnetizable material, and a current which varies in accordance with the sounds to be recorded is passed through the coils of the electromagnet. The electromagnet A, which has a pole a, may be carried on the end of an arm C similar to a gramophone tone-arm, and in the construction shown in Fig. 2, two pins D are adapted to run in adjacent convolutions in the spiral groove b and guide the electromagnet during rotation of the disc b. A horse-shoe magnet may be employed in conjunction with a blank having two parallel spiral ridges b<1>, b<2>, Fig. 3, the magnet being arranged to have one pole over each ridge. If desired, two magnets may be provided in connection with a single disc, one being arranged above and the other below the disc. The end of the electromagnet A may be shielded by a copper disc E, Fig. 4, which is carried pivotally in the forked end of the arm C by means of two screws C<1> projecting into the ends of a recess e<3> in the edge of the disc E. The pole a of the electromagnet projects through a central hole e of the disc E and lies over the ridge in the blank B. The undersurface of the disc E is provided with grooves corresponding to the spiral grooves b in the blank for the purpose of guiding the copper disc over its surface.