GB341647A - Improvements in electro-magnetic vibratory devices such, for example, as loudspeakers - Google Patents

Abstract

341,647. Loud-speakers. MACKINTOSH, E. V., 32, Ernle Road, Wimbledon, London. Dec. 4, 1929, No. 37235. [Class 40 (iv).] In an electromagnetic vibrating device, such as a loudspeaker, having an armature constrained to move in a direction inclined at an angle of less than 20‹ to the co-operating surfaces on the armature and a magnet pole, the stiffness of the armature support is made such that the natural frequency of the vibratory system comprising the armature and the diaphragm or other member to which it is connected, lies in the lower audible range. The construction shown comprises a magnet 1 having polar extensions 2, 3 each terminating in a pair of pole tips 4, 5 and 6, 7 respectively. Coils 8 surround the upright portions connecting the pole tips, the opposed surfaces of which are inclined as shown. The armature structure, comprising armatures 9, 10 connected by rods 11, is secured to thin strips 12, 13 anchored at each to the magnet poles, the strips furnishing the requisite small restoring force. Two opposite surfaces of each of the armatures are inclined as shown, so that these surfaces are parallel to the pole surfaces with which they co-operate. A rod 14 connects the armature structure with a diaphragm 15. According to one arrangement, the angle between the direction of movement of the armature and the co-operating surfaces of the armature and magnet poles is 15‹ and the natural frequency of the vibrating system is approximately 100 cycles per second whilst in another construction the angle is 9‹ and the natural frequency is only slightly in excess of 50 cycles per second. According to a modification, an armature co-operates with one fixed magnet pole and is itself polarized by being arranged in contact, through its supporting means, with the other pole.