GB432603A - Improvements in or relating to apparatus for photographically recording sound - Google Patents

Abstract

432,603. Optical sound - recording apparatus. WESTERN ELECTRIC CO., Ltd., Bush House, Aldwych, London.-(Bell Telephone Laboratories, Inc. ; 463, West Street, New York, U.S.A.) May 11, 1934, No. 14324. [Class 40 (ii)] In optical sound-recording apparatus employing a light valve comprising current carrying ribbons 8, 13 adapted to vibrate in a magnetic field so as to modulate a recording light beam, the ribbons are arranged to have different natural vibration frequencies which are located higher in the frequency scale than the normal range of sound frequencies to be recorded. Thus the natural frequency of one ribbon may be 8000 to 9000 cycles per second whilst that of the other ribbon is 13000 cycles per second. In order to obtain these different natural frequencies, the ribbons may be differently tensioned or mounted or may be of different materials, thicknesses or lengths. The invention is stated to minimize the distortion of the sound record, particularly at high frequencies, the device acting at low sound frequencies more or less as a doubleribbon light valve with equally tuned ribbons whilst at high sound frequencies it acts rather like a single ribbon light valve. If desired, the response of the ribbons at low frequencies may be exactly equalized by connecting an impedance 17 in parallel with the ribbon 8 tuned to the lower frequency or by using a heavier ribbon for the ribbon 8. The invention may be applied to recorders having more than two ribbons and also to recorders in which the ribbons are biassed in accordance with the loudness of the sounds to be recorded in order to produce a noiseless record as described, for example, in Specification 405,078.