GB695435A - Improvements in devices for the stereophonic transmission of music - Google Patents

Abstract

695,435. Directional systems. SCHAEFFER, P. Feb. 11, 1952, No. 3519/52. Class 40 (iv). Sounds are reproduced in a concert hall 1, Fig. 1, by loud-speakers 2, 3, 4, 5 at the vertices of a right pyramid with an equilateral triangular base. The loud-speaker axes coincide at the centroid of the pyramid. The virtual source of sound is controlled by means of a device comprising fixed coils 34 to 37, Fig. 2, at the vertices of a similar but smaller pyramid and with their axes coincident at the centroid. A coil 49, Fig. 4, is wound on a tubular iron core with a spherical polopiece 48 and is energized with current at 5000 c/s. As the coil is moved with respect to the fixed coils, so the virtual source of sound moves with respect to the loudspeakers in the hall. The 5000 c/s. current induced in the coils 34 to 37 is amplified and rectified in stages 53 to provide potentials to control variable mu valve amplifiers 10 and volume expanders 18 in the loud-speaker channels which are fed by a pick-up 8 and an amplifier 9. Each expander is followed by a power amplifier 22. The audience is preferably seated beneath loud-speaker 5 in a circular area with a diameter a/2, where a is the distance between two loud-speakers at the base.