GB381803A - Improvements in or relating to the actuating members of electrodynamic loudspeakers,microphones and the like and the method of manufacturing such members - Google Patents

Abstract

381,803. Sound reproducing and transmitting devices. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN, 13D, Emmasingel, Eindhoven, Holland. Jan. 20, 1932, No. 1801. Convention date, March 7, 1931. [Class 40 (iv).] In an electrodynamic loud-speaker, microphone, or the like, comprising a moving coil for the audio-frequency currents, the coil carrier is formed by one or more layers of non- rigid material such as fabric, paper, &c. which, together with the coil, after the latter is completed, is artificially stiffened. The coil supporting material may enclose the windings of the coil wholly or partially, or it may be embedded between layers of the wire windings, and the arrangement is such that whilst the carrier has relatively little weight, it prevents displacement of the windings. Figs. 1, 2, and 3 illustrate one method of making a coil unit, in which a piece of silk 2, having strips 3 at one end, is first wound on a mandrel 1, and a few layers 4, 5 of wire are wound over the greater part of the piece 2. The strips 3 are folded back over the coil after the outermost layer 8 has been partly formed, and the winding is completed in such a manner that only the central portions of the strips are covered by the outer layer of wire. The extremities of the strips are secured by paper layers 12 wound over the end portion of the piece 2 that is not covered by wire. During this final winding, electrodes 14 are laid between the layers 12 and are welded at the ends of the coil. When the winding is complete, the whole unit is impregnated whilst still on the mandrel, with a lacquer or resin which is then hardened by backing. The mandrel is then withdrawn, one or more layers of oiled paper preferably having been inserted between the silk and the mandrel to facilitate this. In a similar construction, that part of the silk which is not covered by the winding lies over a small transverselycorrugated tube having an exposed conical flange, and instead of the paper layers 12 (Fig. 2) layers of thread are wound over the grooved tube and the intervening silk, so as to clamp the free ends of the silk strips. Further constructions are described, in which a layer of fabric such as silk is provided not at the inner surface of the coil but between two or more layers of wire wound on each side of the fabric. One such modification is shown in Fig. 6, 31 being a layer of silk interposed between only two layers 30 of wire. The silk is secured by thread 34 to a corrugated aluminium tube 35 having a conical flange (as in a construction previously described), which flange serves for attachment of the unit to a conical diaphragm, by electric welding or otherwise. During the manufacture, one' or more layers 29 of very thin oiled paper are first wound on the mandrel 1, and each layer of wire is coated with lacquer or artificial resin, subsequently hardened by heat. The lacquer forms a thickened smooth edge 32.