GB295686A - Improvements in or relating to acoustic devices such as loud speaking telephones - Google Patents

Abstract

295,686. Electrical Research Products, Inc., (Assignees of Schlenker, V. A.). Aug. 17, 1927, [Convention date]. Diaphragms; loud-speakers; magnetic instruments.-A diaphragm for sound radiators, more particularly of the direct-acting type, is provided with tapered lumped impedance elements distributed on its surface, the impedance elements and diaphragm constituting the elements of a low pass mechanical filter. In the construction, Fig. 2, a diaphragm 10, formed of a metallic alloy composed of approximately 98¢ per cent aluminium and 1¢ per cent manganese and of a thickness less than 0.005 inch, is maintained under high tension by a frame 11 and a clamping ring 12 secured to the frame by screws 13. Loading masses or impedances in the form of circular or square brass ,weights 30-42 are cemented or glued to the diaphragm as shown. In a modified construction, Fig. 4, the loading masses 40- 43 are spherical in cross-section and are preferably attached on both sides of the diaphragm 44, whilst in a further modification, Fig. 5, the loading is applied in the form of circular segmented rings 46-49 applied to one or both surfaces of the diaphragms 45. The diaphragm according to the invention is analogous to an electrical filter in that the masses of loading are comparable to the series inductance of the filter and the thin surfaces of the diaphragm are comparable to the shunt capacities. The diaphragm 10, Fig. 2, is driven by an electrodynamic unit 16 supported by cross-members on the frame 11, the coil 17 positioned between the annular magnet pole-faces 18, 19 being attached to the diaphragm so that its axis is offset from the centre thereof approximately two-tenths of the diameter of the inner radius of the loading masses. The frame 11 is attached to a baffle or partition 21 placed in a cabinet 22, protective screens 23 being positioned in the openings in the front and back of the cabinet.