GB312950A - Improvements in loud speakers and the like - Google Patents

Abstract

312,950. Lucas, O. D. Feb. 1, 1928. Diaphragms; magnetic instruments. - The coil of a moving coil loud-speaker &c. extends into two annular magnetic air gaps in such a manner that in addition to these air gaps there is a further air gap or gaps separating the inner poles and/or outer poles at the centre of the coil. In the construction, Fig. 1, the coil a carried by a cylinder g moves coaxially over cores c, b of opposite polarity provided with energizing coils e, d and supported at their outer ends on a soft iron pot h provided with an inner extension h<1> which forms the outer member of the annular air gaps. The cylinder g is suspended on a disc or radial arms f carried by a rod i which is secured to a cone m and is suspended by loops j, k of silk &c. Alternatively, the arms f may extend through slots in the pot h and be secured to the cone m as shown in Fig 2. In this modification, the annular magnetic fields are formed between a common core c and annuli c<2>, the ends of the core being secured to discs c' which are connected to the annuli c<2> by rods c<3> on which are wound energizing coils c'. The magnet within the cone m is covered by an inverted cone m<1>. The single coils d, e or c<4> may be substituted by three or more connected in series or parallel. According to a further modification (Fig. 3, not shown) the coil a is divided into two portions connected in series and located in annular fields of opposite polarity formed by two pot magnets. The cone' m may be suspended at each end by loops similar to j, k, Fig. 1, the distance of the points of suspension from the axis of the cone being preferably equal to the diameter of the base of the cone. Instead of the central cores being of equal length with an energizing coil on each, the core remote from the cone may be made considerably longer than the other so as to carry a single coil.