GB290239A - Improvements in or relating to acoustic devices such as loud speakers - Google Patents

Abstract

290,239. Electrical Research Products, Inc., (Assignees of Harrison, H. C.). May 11, 1927, [Convention date]. Loud-speakers; diaphragms; magnetic instruments. - An acoustic device comprises a long .direct acting diaphragm tensioned in the direction of its length only and to such a degree that the velocity of propagation of transverse waves therein in this direction is greater than one-fourth the velocity of sound in air. Preferably, the diaphragm is tensioned to such a degree that the velocity of propagation therein is substantially equal to that of sound in air so that sound waves radiated from various portions thereof along a line extending in the direction of its length are substantially in phase. The length of the diaphragm is preferably greater than twice its width and also greater than half the wave length of the lowest frequency to be radiated. The driving element for the diaphragm is connected thereto by means of a distributing system adapted to propagate energy therethrough at a velocity comparable with that of propagation of sound in air. In the construction shown, the flat diaphragm 11 has its lower edge clamped by screws 14 between the serrated surfaces of a member 13 and of a projecting portion 12 of a frame 10, the upper edge of the diaphragm being similarly clamped between the serrated surfaces of members 15, 16 by screws 17. Rods 18 secured to the member 15 and passing through holes in a projecting portion 19 of the frame 10 are provided with compression springs 20 and nuts 21 for tensioning the diaphragm. Damping strips 40 of felt &c. connect the edges of the diaphragm with the frame 10. An electromagnetic unit 22, secured to cross members 23, 24 on the frame 10, is connected with the diaphragm by means of a rod 30 and arm 29 which is rigidly secured to a tubular member 25 extending parallel to the diaphragm between its opposite edges. Diametrically opposite portions of the member 25 are connected by narrow strips 26, 27 of flexible material such as paper, to the diaphragm and a rigid support 28 respectively. The strips 26, 27 may either be continuous, or a plurality of separate strips may be used. The Specification as open to inspection under Sect. 91 (3) (a) describes a modification in which a driving element is connected to a long laterally pleated diaphragm, secured at its periphery, by means including a tubular member extending in the direction of its length. This subject-matter does not appear in the Specification as accepted.