Patent GB-253159-A (GB)
Title: An improved loud speaker
IPC: H04R11/00
Filed: 1925-02-04
Abstract: 253,159. Sykes, A. F. Feb. 4, 1925. loud-speakers ; Magnetic instruments; diaphragms. - A loud-speaker or the like comprises an armature, consisting of or containing magnetic material, supported in a magnetic gap and a winding or windings contained within a slot in either or both polar faces or in the armature or adapted to cause or be excited by movement of the armature. in a direction at right angles to the field by strengthening the field in the armature at one edge of the gap and weakening it at the other edge of the gap. When two windings are employed, one of the windings may be employed to damp the vibration of the armature. The armature may be attached to the diaphragm, which may be fixed or free at its outer edge, either at a number of points or on a line or surface of attachment and with or without a spacing member. Fig. 1 (Prov.) shows a construction in which a ring-shaped armature 300, attached by a single or double flange 301 to the diaphragm 302 is located in an annular gap between the inner and outer poles 9, 10 of a magnet 7, the control windings 116 being located in slots in the magnet poles. The armature may also be supported so as to prevent lateral movement thereof by means of a number of springy strips mounted on washers on one of the magnet poles. Fig. II shows a construction in which the control winding 1 is mounted in a slot in the ring armature 300, a spacing member 275 being provided between the armature and diaphragm. The armature 300 may be slotted on both sides or may be made to enclose the coil completely. Fig. 1 (Comp.) shows the electromagnetic instrument 368 mounted on a bracket 370, the armature being connected to the apex of a conical diaphragm 369. A number of ways of securing the armature to the diaphragm are described, one oi which consists in providing the armature with a number of projections adapted to be passed through holes in the diaphragm and either riveted over or secured by an adhesive, such as shellac. The periphery of the diaphragm may be secured by a rubber ring 49, the edge of which is secured by twine in a groove in a ring 253 on the bracket 370. In a modification, the bracket 370 takes the form of a vertical plate having a number of openings, the periphery of the diaphragm being secured to a wooden ring united to the bracket. In the construction, Fig. III, the instrument 368 is mounted in a box 373, the front of which is closed by the diaphragm 369, which, as shown, is of curved form with a re-entrant dome-shaped portion 374. The armature 300 is connected at the junction of the portion 374 with the main portion of the diaphragm. Fig. V shows a construction in which the armature 300 is secured to the conical diaphragm 378 at a point about midway between the apex and base of the cone, the outer magnet pole being provided with the annular extension 379. In a further modification, Fig. VI, the diaphragm 380 is of the annular form described in Specification 227,162, the armature 300 being secured thereto on a ring intermediate between its internal or external circumferences. The diaphragm may be curved or V-shaped in cross-section. The sound passage 105 in this construction is arranged in the central magnet pole. Further modifications are described in which a relatively large diaphragm is actuated by a plurality of armatures, which may ur may not be arranged concentrically. The armature 300 is not necessarily ring-shaped, and Fig. VIII shows a bar armature supported on the diaphragm 302 and spring strips 304 in a gap between the magnet poles. More than one bar armature may be employed and these may be arranged parallel to one another in a triangular formation or radially. The diaphragms may be made of mica, cork, hard paper, cardboard, cellulose or textile fabric impregnated with a stiffening agent, such as shellac or artificial resin. Specification 127,669 also is referred to.