Patent GB-271405-A (GB)
Title: Improvements in loud speaker unit
IPC: H04R11/00
Filed: 1927-01-18
Abstract: 271,405. Baltzley, L. E. May 20, 1926, [Convention date]. Loud-speakers; magnetic instruments; diaphragms.-An electromagnetic actuating unit for a loud-speaker of the horn or large diaphragm type, comprises the combination of a U-shaped or like bi-polar magnet having pole-pieces extending to opposite sides of an armature, the armature system comprising a thin strip of elastic material preferably tensioned between two end supports and extending through the gap between the magnet poles. In the constructions described, the strip supports an armature secured thereto, so as to lie along the strip and between the ends thereof. Means are also preferably provided for varying the tension of the strip. The magnet structure, Figs. 1 - - 4, comprises a horseshoe magnet 10 having pole pieces 11, 12 secured to its respective ends by washers 18 and bolts 19, which also serve to secure the magnet to a supporting base 21. Each pole piece is formed with parallel side portions 13, 14, Fig. 4, integrally connected by a diagonal brace 15, the portion 13 being arched downwardly as at 16 below the armature level and the portion 14 being arched upwardly as at 17 above the armature plane to provide an arrangement of polar projections 11<a>, 11<b>, 12<a>, 12b as shown in Fig. 5. The actuating coil 43 is carried by a spool 44 which is clamped between the cheeks 16, 17, against positioning lugs 45 thereon, by screws 46. In order to allow the pole tips to be spaced the correct distance apart after assembly, small taper screws 70 may engage with companion screw seats 71 in the superposed polar projections, the screws acting as fine wedges to force the pole tips apart or separating screws mounted in a screw seat on the edge of one pole tip may be adapted to bear upon an extension lug of the opposing pole tip below. The armature 22 is positioned within the gaps between the polar projections by mounting it on a thin strip 27 of elastic material, such as phosphor bronze, the ends of the strips being secured tc blocks 28, 29 secured by screws 30, 31 on the inclined seats 32, 33 on a raised central portion of the base 21. Screws 34. 35 bearing on the inner ends of the blocks 28, 29 enable the blocks to be tilted so as to position the strip centrally in both gaps. The strip 27 is tensioned by a screw 36 acting on a cross bar 37 which presses a bight in the strip more or less into a cavity 38 in the block 29. The armature 22 is connected by a rod 23 to a sound reproducing diaphragm, the outer end of the rod being preferably guided by passing it through a sleeve lined with felt &c. Fig. 7 shows the actuating unit employed in a loud-speaker of the large conical diaphragm type, the sleeve 49 for the rod 23 being carried by an arm 62 having its other end secured beneath the screw 30. Various ways of securing the arma. ture 22 to the strip 27 are described. In the construction, Figs. 5 and 6, the strip is formed with a wide slot 39 in the region of the magnet poles and a narrower slot 40 extending therefrom substantially to the block 28. The armature is formed of such a width as to pass freely into the slot 39 and is grooved in its sides as at 41 so as to slide into the slot 40 in which it is secured by soldering &c. In the modified construction, Fig. 10, the slot 39a in the strip has a restricted intermediate portion 40<a> to the edges of which the armature is secured, the rod 23 being connected to this centrally attached portion. In a further modification, Fig. 11, the armature is secured to the strip in a manner similar to that shown in Fig. 10 but the area of engagement between the armature and strip is of less length and the magnet system is polarized as shown so as to effect a rocking movement of the armature. The rod 23 is connected with the armature, in this case, at a point just outside or inside one of the pole cheeks. Fig. 13 shows a construction in which one of the supporting blocks 51 for the strip is adapted to be moved longitudinally by means of a screw 54 in order to adjust the tension of the strip. When, as shown in Figs. 1 and 5, the armature is of greater length than the polar structure of the magnets, the part of the armature which extends beyond the magnet poles may be of non-ferrous metal. The Specification as open to inspection under Sect. 91 (3) (a) comprises also a construction, Fig. 15 (Cancelled) in which the armaturecarrying strip 27 is tensioned between end sup. ports 66, 67 on a receiver unit of the bi-polar type. The cup shaped base may, if desired, be replaced by a base in the form of a spring yoke having projections to enter openings in the ends of the strip so as to impart the desired longi. tudinal tension to the strip. This subject. matter does not appear in the Specification as accepted.