Patent GB-465795-A (GB)
Title: Improvements in electro-acoustical reproducers
IPC: H04R7/12
Filed: 1935-11-08
Abstract: 465,795. Sound - reproducers. GROVES, W. W. (Cinaudagraph Corporation) Nov. 8, 1935, No. 30936. [Class 40 (iv)] An electro-acoustic reproducer comprises a cylindrical voice-coil structure, a diaphragm structure constituted by an inner high-frequency member rigidly connected to the voice-coil structure and having a portion extending radially within the circumference of the voicecoil, a substantially conical low-frequency member, and a compliance ring, formed of a material having a different physical structure from that of the low-frequency member, which is connected to the inner high-frequency member and which is interposed between the high-frequency and low-frequency members, and centring means connected to the diaphragm structure and extending outwardly. relative to the diaphragm structure and the voice-coil. The high-frequency portion has peripheral portions 23, 24 between which is a V-shaped portion 33 rigidly connected to a cylindrical former 21 of mica located in an annular gap, between centre and outer polepieces 10, 12 respectively. The mica has longitudinal cracks 31 to facilitate its formation into the cylindrical shape and the speech coils 28, 29 extend beyond the inner surface of the polepiece 12. The portions 23, 24 of the diaphragm have circumferential flanges 25, 26, and adjacent the junction of the portion 33 with the mica cylinder is attached by means of a felt ring 20 a low-frequency cone 9 comprising a portion 16 of soft fibrous paper to which is secured a reinforcing layer 32 of soft fabric, e.g. chamois or rubberized cloth. The coil is centred in the gap by a spider, Fig. 3, comprising a central ring 37 formed with rings 38 having side portions 39, 40 bent upwardly to limit the bending to the area adjacent the ring 37. The spider is attached to the cone housing by bushes 42 and resilient blocks 44, for example, of sponge rubber. The cone 9 may be of unitary construction, the inner portion being roughened and the outer portion stiffened, e.g. by lacquering. A dome-shaped member 75 provided with a lining 76 of felt or other sound-absorbing material is attached to centre pole-piece 10 to prevent undesired resonance in the air chamber formed by the high frequency member 9<1>. The loud-speaker is mounted in a cabinet 34 having its walls lined with batting 35. In a modification of Fig. 1, Fig. 5 (not shown) the portion 24 of the diaphragm shown in Fig. 1 is continued to form a dome and the portion 16 of the cone 9 is not continued as far as the coil-former 21, the compliant connection being formed by the removal of a portion of the member 16 from the member 32. Fig. 6 shows a further modification of Fig. 1, in which the portion 24 is extended to form a dome 50 and the portion 23 is attached to a rubberized fabric-cone 32 to which the paper cone 16 is secured, The coil is centred by cords 64 attached to the corners of a regular polygon formed by strings 62 whose middle points are attached to the coil-former 21. A channel 60 in the centre pole-piece 10 relieves the pressure in the chamber 61 beneath the dome 60. Modified forms of the resilient coupling between the portions 23 and 32, Figs. 8, 9 (not shown) comprise a conical ring of felt, or a narrow ring of compliant material additional to the ring 20 shown in Fig. 1. In a further modification, Fig. 10, the cone C is formed as a single unit, the inner and outer parts 100, 101 being formed as deposits on a suction screen from suspensions of wood fibres, and wool, cotton or rayon fibres respectively. The fibres of the portions are interwoven and felted over a region 102 to form the compliant connection between-the high and low frequency portions 100, 101 of the diaphragm. The relative degrees of stiffness of the portions are effected by impregnation or coating with a lacquer. Alternatively, the cone may be made from a single material, the parts 100,101 being subjected to impregnating and moulding operations to provide the relative degrees of stiffness, and a zone 102 of the untreated material itself forming the compliant connection. The cone is supported and the voice-coil centred by a corrugated ring 104 of stiffened cheese-cloth or gauze or of solid material formed with openings to relieve the air pressure between the ring and pole-piece 108. Reference has been directed by the Comptroller to Specification 451,178.