GB432811A - An improved method of, and apparatus for, recording sound - Google Patents

Abstract

432,811. Recording sound. RADIO CORPORATION OF AMERICA, 30, Rockefeller Plaza, New York, U.S.A. Feb. 5, 1934, No. 3739. Convention date, Feb. 24, 1933. [Class 40 (ii)] Relates to soundrecording apparatus in which the sound waves impinge on a diaphragm which directly effects the recording. According to the invention, in usng such a device for producing a variable-width photographic record that gives a minimum of background noise on reproduction, the diaphragm is biassed by a pressure dependent on the volume of the sound being recorded. The invention is stated to be applicable also to recording by means of a phonograph stylus or the like. As shown, a diaphragm 20 in a sound-box 10 is connected bv a rod 22 to the vibratory support 23 of a light-reflector, which may be a lens mirror (not shown). Using an optical system of the ordinary kind, light is reflected from the mirror through a slit on to a photographic film. The back 25 of the soundbox has an aperture 26, covered by a resilient flap 27, and the rod 22 is surrounded by a rubber &c. washer 28 where it passes through the back 25, to prevent air leakage. When sounds of large amplitude vibrate the diaphragm, air escapes past the valve 27, producing a large biassing pressure on the diaphragm, since the rate at which air returns to the chamber behind the diaphragm is small. With sounds of relatively small amplitude, little air is ejected through the valve 27, and the bias pressure is low. Thus, the arrangement produces a record such as is shown in Fig. 2, the zero line of the oscillations being shifted in accordance with the amplitudes.