GB339312A - - Google Patents

Abstract

339,312. Abrahams, A. I. May 21, 1929, [Convention date]. Magnetic instruments ; diaphragms. -A moving-coil loudspeaker unit comprises a casing, a diaphragm located therein having three concentric zones disposed in angular relationship to each other, the inner zones projecting from the peripheral zone towards the open end of the casing, the wall of the casing adjacent the diaphragm being shaped so that the passage between the wall and the diaphragm has an increasing cross-sectional area, preferably according to an exponential formula, from the periphery of the diaphragm to the open end of the casing. Fig. 1 shows a construction employing a magnetic casing 1 provided with a central core 3 and cap 4 forming an annular air gap in which is located a coil 6 secured to the diaphragm D. The diaphragm, shown more clearly in Fig. 2, is preferably stamped from a very light and strong aluminium alloy and is provided with a peripheral :flange 7, and intermediate frusto-conical portion 8 and a stiff central conical or convex portion 9 formed with flutes or corrugations 10<a>. A flexible member 10 of non-stretchable and impregnated cloth is cemented to the flange 7 and portion 8 of the diaphragm and is clamped between gaskets G connected to a member 11 mounted on the cap 4. If desired, tha outer diameter of the flange 7 may be the same as that of the member 10 so that that gaskets are clamped upon both metal and cloth. Binding posts connected to the coil 6 are provided on the member 11 which carries a throat portion T externally threaded at 14 to receive an exponential horn. The coil 6 is carried by a non- metallic support 18 cemented to the inner side of the diaphragm. The coil mount may be made of an impregnated strong linen cloth, stiffened by several coats of lacquer, of the material known under the registred Trade Mark " Bakelite," or of a thin, light, stiff paper, such as manuscript paper. When made of cloth or paper, the mount may be cut with serrations S and the diaphragm mount 10 may be similarly formed. According to a modification, the central portion 9 of the diaphragm may be dome-shaped, with or without corrugations. The diaphragm is first mounted on the member 11 which is then secured to cap 4 after which this sub-assembhis mounted on the casing 1. Specification 312,603 is referred to.