GB357957A - Improvements in or relating to wave signalling systems - Google Patents

Abstract

357,957. Acoustic delay apparatus. STANDARD TELEPHONES & CABLES, Ltd. and SANDEMAN, E. K., Columbia House, Aldwych, London. June 19, 1930, No. 18699. [Class 13.] An acoustic delay device for use in electrical signalling systems comprises a fluid chamber with a transmitter at one end and a receiver at the other, means being provided for communication between the fluid and the outer atmosphere or a sound-absorbent material on the outer wall of the chamber so that the attenuation of waves passing through the chamber may be modified. The chamber may comprise a brass tube 11, Fig. 2, containing air, carbon-dioxide, water, &c., depending on the speed of propagation required. The attenuation means, which is provided to avoid distortion introduced by acoustic reflections in the tube, may consist of absorbing material 15 housed by a cover 16 outside an aperture 14 in the tube or of gauze 17 covering the aperture, which may be a slot tapered towards its ends, or a series of holes similarly tapered. In use signals from a line L, Fig. 1, are transformed into vibrations of a diaphragm 2, by electromagnetic means 1, and the acoustic waves pass along the fluid tube 4 to a diaphragm 6 actuating a microphone 7 which sends electric signals through an amplifier 8, attenuation equalizer 9, and compensating amplifier 10, to the line L<1>. Chambers 3, 5 are provided for match. ing the impedances of diaphragms 2, 6 with the fluid tube 4.