GB956362A - Electro-acoustic transducer assemblies and methods of manufacturing resonance-damping cover walls therefor - Google Patents

Abstract

956,362. Telephone instruments. SONOTONE CORPORATION. July 4, 1960 [July 6, 1959], No. 23265/60. Heading H4J. An electro-acoustic transducer assembly ineludes a housing enclosing a transducer 21 (Fig. 1) and a vibratory diaphragm 64, the housing having a cover wall 70 (Figs. 4, 5) that defines with the diaphragm 64 an enclosure communicating with the exterior of the assembly through a series of apertures in the cover wall, each aperture comprising a slot 71 defined by the opposite edges of a slit cut in the cover wall, the opposed edges of the cut slit being displaced relative to each other by an amount exceeding the thickness of the wall material, and the width of the slot 71 so formed being less than the thickness of the wall material such that it provides a significant degree of damping to acoustic resonances of the diaphragm 64. The slots 71 are made by cutting a series of slits in a sheet-metal blank, bending the material defining at least one edge of each slit out of the original plane of the blank, and bending the material back towards its original position. Each edge of each slit may be first bent in opposite directions out of the original plane of the blank and subsequently bent back inwardly to define a slot 79 (Figs. 11, 12, not shown). The slots are of width 0.0005 to 0.003 inch. The device is a microphone and transducer 21 is a piezo-electric element coupled to diaphragm 64 by a stirrup 66. The wall 70 may have one or more stiffening ribs 78. The circular rim 74 of wall 70 is secured by cement to a housing 60 and to the periphery of the diaphragm 64. Alternatively, or in addition, rim 74 is retained in position by a flange 68 of an elastomeric casing 69. The dimensions of the slots may be checked by holding the wall 70 in a jig and feeding gas under pressure through the wall 70 while measuring the pressure difference on a gauge connected across the two sides of the wall 70 (Fig. 10, not shown).