GB336930A - Improvements relating to electro-magnetic units for acoustic instruments - Google Patents

Abstract

336,930. Ruppert, J. April 10, 1930. Magnetic instruments. - An electromagnetic unit for acoustic instruments, more particularly a driving unit for large diaphragm loud-speakers, comprises outer and inner magnetic poles on both sides of the axis of vibration of an armature, the arrangement being such that the outer poles exert on the armature a turning moment which is in opposition to that exerted by the inner poles with the result that the amplitude of vibration of the armature is proportional to the difference between the opposing moments. In the construction shown, the armature 9 is centrally mounted by lateral extensions 10, 11 between the pole pieces N1- - N4 and S1 - -S4 of laminated pole shoes 3, 4 which bridge the like poles of two permanent horseshoe magnets 1 of substantially equal intensity of magnetization. The pole shoes are secured to the magnets by screws 3a, 4a so that the correct spacing of the pole shoes is obtained by placing the holes for the screws in appropriate positions in the magnets. Speech coils 5, 6 are accommodated in the outer recesses of the pole pieces, the input leads being attached to terminals on a. strip 7. One end of the armature is connected to a conical diaphragm by rod 13, adjustable springy strip 14 and rod 15. In operation, the coils are so arranged that the currents therein produce magnetic poles n1, s1, n2, s2 in the armatures as shown in Fig. 4 with the result that the turning moment exerted by the outer poles N1, S1, N4, S4 is damped by the lesser opposing turning moment exerted by the inner poles N2, S2, N3, S3.