GB308318A - Improvements in or relating to acoustic devices - Google Patents

Abstract

308,318. Marconi's Wireless Telegraph Co., Ltd., (Assignees of Ringel, A. S.). March 21, 1928, [Convention date]. Magnetic instruments; diaphragms. - An acoustic device, such as a loudspeaker, comprises a diaphragm having portions whose maximum responses occur at different frequencies or over different frequency ranges and eddy current means for vibrating the portions s simultaneously whereby a substantially constant response is obtained over a wide frequency range. The figure shows a loud-speaker employing a conical or frustum-shaped diaphragm 54 having its larger end supported by a ring or strips 11 of resilient material in an opening in a baffle 3. 'The diaphragm is actuated by copper, aluminium &c. sleeves 52, 57 secured to the diaphragm, as shown, and located in annular air gaps 61, 62 between the pole pieces 58, 59, 60 of a permanent electromagnet 49. Speech coils 51, 53 are provided in the pole pieces 59, 60 and the sleeves 52, 57 are made as light as possible by cutting out portions 56 therefrom. The sleeve 52 is stated to produce a greater response to low frequency vibrations, when the cone vibrates as a whole, while sleeve 57 will be more responsive to high frequency vibrations producing nodes and antinodes along the length of the cone. This action of the sleeves may be aided by permitting only the lower frequencies to flow in the outer winding 51 while the higher frequencies are confined to the inner winding 53. Specification 311,486 is referred to. The Specification as open to inspection under Sect. 91 (3) (a) comprises also an arrangement in which the sleeves 52, 57 are replaced by a pair of coils, the coils 51, 53 being dispensed with. This subject-matter does not appear in the Specification as accepted.