GB1270033A - Louspeaker - Google Patents

Abstract

1,270,033. Diaphragms; moving coil loudspeakers. NIPPON GAKKISEIZO K.K. 9 May, 1969, No. 52064/71. Divided out of 1,270,032. Heading H4S. A loud-speaker includes a rigid self-supporting diaphragm 21 (Fig. 3) of foamed plastics material secured at its periphery to a speaker frame 22 to generate sound by bending motion. Soft material 27 (e.g. foamed or unfoamed rubber or rubber-like material) having a specific gravity in the range 0À1 to 1À25 is applied to the diaphragm 21 at the periphery and has sufficient mass to prevent harmonics of the resonant frequency of the diaphragm from being developed in the frequency range of about 70 to 150 Hz. The material 27 may be attached around the whole or part of the periphery of the diaphragm. It may be on one or both faces of the diaphragm. There may be a small space between it and the loud-speaker frame (Fig. 6, not shown). It may be of uniform cross-section throughout the periphery or the cross-section may vary. The diaphragm is preferably of foamed polystyrene of specific gravity 0À02 to 0À20. The total weight of soft material 27 is 20 to 200% of the total weight of the diaphragm, e.g. 100%. A polyvinyl sheet may be applied to the front sheet of the diaphragm to improve its flexural rigidity and internal frictional loss. The diaphragm 21 may be attached to the frame 22 by a cushion of tape 26. The diaphragm is preferably of asymmetric shape, the soft material 27 having a larger width in the direction of the major axis than in the direction of the minor axis (Fig. 5, not shown). Additional foamed or unfoamed rubberlike elastomer 58 (Fig. 8) may be superimposed on the soft material 57. Soft material in the form of adhesive tape 67 (Fig. 9) may join the diaphragm 61 to the speaker frame 62. In a modification of the embodiment of Fig. 9 the outer edge of the diaphragm may be aligned with the inner edge of the frame (Fig. 12, not shown) so that the diaphragm cannot act as a piston. Alternatively, soft material 87 (Fig. 13) is secured to the speaker frame 82 and the edge 83 of the diaphragm 81 terminates midway of the attaching surface 85 of the speaker frame 82. An adhesive 86 of soft foamed plastics material, such as foamed polyurethane, is adhered to the diaphragm 81.