Patent GB-430921-A (GB)
Title: Improvements in or relating to electro-acoustic translating devices such as loudspeakers
IPC: H04R1/26
Filed: 1933-12-27
Abstract: 430,921. Loud-speakers. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Bostwick, L. G.; 39, Hedges Avenue, Chatham, New Jersey, U.S.A.) Dec. 27, 1933, No. 36416. Convention date, Jan. 6. [Class 40 (iv)] [See also Group XL] An electro-acoustic translating device, such as a loud-speaker, has the periphery of its diaphragm secured to a support by an annular flexible mounting which includes a corrugated portion, the corrugations being substantially linear and arranged in polygonal formation around the periphery of the diaphragm. If desired, the annular mounting may be formed integral with the diaphragm. Figs 1 and 2 show a construction of moving coil loudspeaker, adapted more particularly for low frequency response, in which the periphery of the paper cone 24 is supported by an annulus 37 formed of the material known under the Registered Trade Mark " Duralumin " and comprising a plurality of sectors separated by radial slots 38 preferably sealed by felt strips 45. Each sector comprises a serrated flanged portion 39 secured to the edge of the diaphragm, a flat peripheral portion 40 seated between paper washers 43 on a flange 42 on the frame 22 and an intermediate flexible portion 41 formed with parallel linear corrugations 44 arranged in polygonal formation about the periphery of the diaphragm. The cone is driven by a moving coil 26, the end portions 27 of which extend along the former 25, as shown in Fig. 3, to terminals 28 secured to the inturned flange 30 of the former and the coil is centred in the air gap by resilient members of the form shown in Figs. 2 and 3, the outer fingers 32 being secured to flange 30 and the intermediate fingers 33 to studs 35 on the centre magnet polepiece 17. The loud-speaker assembly is mounted within a closed casing 46, the rear wall 49 of which is adjustably mounted on threaded spindles 50. The arrangement is preferably such that the volume of air in the chamber and the mass of the diaphragm and associated moving parts are so proportioned that the resonance frequency of the diaphragm and its associated moving parts is below 100 cycles and their mechanical impedance at this frequency is substantially equal to the mechanical motional resistance of the diaphragm-actuating means. Fig. 5 shows a modified construction of diaphragm comprising a relatively rigid central radially fluted portion 53, a peripheral portion 54 and an intermediate flexible portion 55, the coil former 56 being secured to the apices of the triangular pyramids formed by the radial flutes. Radially extending slots in the diaphragm are preferably sealed by felt strips 59 and the intermediate portion 55 is formed with a plurality of parallel linear corrugations 60 arranged in polygonal formation about the central portion 53. The loudspeaker shown in Fig. 1 may be used in a multi-unit loud-speaking apparatus as shown in Fig. 6 in which each of a pair of casings 61 is fitted with a low frequency loud-speaker 62 of the construction shown in Fig. 1 and a high frequency loud-speaker constructed as described in Specification 361,976. A horn speaker 64 for reproducing intermediate frequencies may be disposed adjacent the casings 61 as shown. Such an arrangement is connected to an amplifier through the multichannel filter network shown in Fig. 7 in which the leads 65 from the amplifier are shunted by an inductance 66 and auto-transformer 67, the latter being provided with a pair of taps for connection to the low frequency speakers 62. An auto-transformer 68 and a condenser 69 are also connected across the leads 65 as shown and another inductance 70 and condenser 71 are connected in series and shunted across a portion of transformer 68, a series condenser 72 being connected to one terminal of inductance 70. The terminal conductors 73, 74, 75 are connected as shown, the conductor 74 forming a common lead to one terminal of each of the high and intermediate speakers 63, 64 and the conductors 73, 75 forming respectively the leads to the other terminals of the high and intermediate frequency speakers.