Patent GB-1157463-A (GB)
Title: Loudspeaker Assembly.
Inventor: SCHOENGOLD HERBERT
IPC: H04R9/06
Filed: 1966-08-02
Abstract: 1,157,463. Loud-speakers. ELECTRONIC RESEARCH ASSOCIATES Inc. 2 Aug., 1966 No. 34569/66. Heading H4J. A loud-speaker assembly comprises a substantially flat diaphragm supported at its edges by a frame which is acoustically compatible therewith, the frame and the diaphragm being composed of plastics material, one or both being of cellular plastics material, e.g. cellular polystyrene. The materials of the diaphragm and support frame are matched acoustically to reduce undesired resonance effects, whilst providing a lightweight assembly. A method of assembling such a loud-speaker is described. In one embodiment, the diaphragm 2, Figs. 2 and 3, is substantially flat and is moulded integral with the rectangular frame 4, which is slightly thicker than the diaphragm. The frame also comprises ribs 6 which support the magnet assembly and diagonal reinforcing ribs 10. The ribs 6 and 10 and frame are shaped so that sound is projected forward or backward from the whole assembly. The magnet assembly comprises a magnetic element 8 acting on a coil formed on former 20 made as a plastics coated paper tube secured to the diaphragm 2, preferably by being embedded in it, together with a reinforcing plate 22 of plastics impregnated fibrous material, which is bonded or formed integral with former 20. The leads 24 to the coil are embedded in the diaphragm and are folded back as at 30 to provide unrestricted oscillation of the diaphragm. Reinforcing layers 3 of plastics or plastics impregnated paper or fabric, or metal foil, are provided on the outside of the diaphragm. The diaphragm may have a number of circular grooves (36) at its edge adjacent the frame portion to improve elasticity, Fig. 5 (not shown). If the frame is formed separately from the diaphragm, it may be made of plastics material somewhat more dense than the diaphragm material, which is of cellular plastics having a density of 0.8-10 pounds/cubic foot. Alternatively, the frame is of cellular plastics and the diaphragm of a different plastics material. The frame may be mounted using rubber mounting cushions in channel support members (33), Fig. 4 (not shown), to which is attached the speaker fabric, or the fabric may be attached direct to the moulded frame. Method of moulding and assembling. Fig. 6.- On to a cylindrical locating member 52, mounted in the mould 54, is fitted the reinforcing plate 22 and coil former 20 carrying the coil. The magnetic assembly, comprising ceramic or Alnico magnetic element 8, top and bottom plates 46, 48 and central member 44 which, with plate 48, forms the air gap, is then positioned by engaging the hole in member 44 over locating pin 56. Cellular plastics material is then introduced to form the diaphragm and frame, fixing the coil and associated wiring and the magnetic assembly in accurately associated positions. The locating member 52 is removed and the hole remaining in the diaphragm filled by plastics plug 58, Fig. 3. Alternative arrangements.-In Figs. 7, 8 (not shown), the reinforcing and magnet carrying ribs of the frame are of a different configuration and are formed of metal. In Fig. 9 (not shown) the diaphragm is driven by four magnetic assemblies and is useful in high output power applications. In Fig. 10 (not shown), various sealing means of rubber, plastics &c. around the magnetic assembly, provide for a moisture proof assembly, for outdoor or even underwater use.