GB1366613A - Electroacoustic transducers - Google Patents

Abstract

1366613 Moving armature transducers INDUSTRIAL RESEARCH PRODUCTS Inc 14 Feb 1972 [17 May 1971] 6760/72 Heading H4J In an electroacoustic transducer gradual or soft saturation of the armature system is obtained to reduce armature clatter or ringing caused by the armature striking the magnets. The armature system includes an elongate magnetic armature 23 having a vibratable end 25 and a pivot end 27. Magnets 33, 35 (Figs. 1, 2) and a coil 21 are for causing the armature 23 to vibrate. The pivot end 27 of the armature 23 is mounted on a base plate 15 and flux conductive legs 29, 31 (Fig. 3) extend transversely from the pivot end to develop a force tending to restore the armature 23 to its neutral position. The crosssectional dimensions of the legs 29, 31 are less than the cross-sectional dimensions of the armature 23. A first flux path for the armature system is traceable from the pivot end 25 of the armature 23 through the legs 29, 31, the base plate 15, the magnets 33, 35 to the free end 25 of the armature 23 to provide a low reluctance path for flux flow, the legs 29, 31 being magnetically saturated before the armature 23 saturates. A second and higher reluctance path is established from the pivot end 27 of the armture through a gap formed by an elastomeric material 69 (Fig. 4) between the region of the pivot end 27 and the base plate 15 when the first flux path saturates. The pivot end 27 of the armature 23 is held by a wire clip 67 (Fig. 4) which elastically clamps the armature end 27 on a pivot support which in turn is spot welded on base plate 15. The elastomeric material 69 prevents metal-tometal contact. Diametrically opposed trapping members (66, 68), Fig. 7 (not shown), may limit movement of the armature system, and blocks (70, 72) may dampen movement of the legs (29, 31). In an altenative armature system (Fig. 10, not shown) the legs are in a plane perpendicular to the armature and the characteristics of the armature system may be changed by trimming the top surfaces of the legs. In another armature system (Fig. 11, not shown) the legs (29B, 31B) each extend only as an arc of a ring and are fixed to plate 15 at spaced points yet another armature system (Fig. 11a) not shown has an arcuate piece of spring material fixed at a mid-point to the pivot end of the armature. The armature end 25 is connected by a drive pin 47 to a cone-shaped diaphragm 63 (Fig. 9) formed with an outer skin of metal or plastics film 95, 97. The interior is filled with hollow plastics spheres 99 lightly coated with adhesive to produce a rigid mass. The free end of drive pin 47 is cemented into the mass of spheres. A surround 71 secures the diaphram 63 to the base plate. The transducer includes a cup-shaped case (75), Fig. 8 (not shown), having a cover 79 into which the motor fits diagonally. A front cavity (87) is open to atmosphere through ports (73). A back cavity (89) is vented through ports (76) covered with cloth (78) to improve low frequency response. The device may be used as a transmitter or receiver.