GB839585A - Improvements in loudspeakers - Google Patents

Abstract

839,585. Loud-speakers. PARMEKO Ltd. Dec. 10, 1958 [Dec. 10, 1957], No. 38346/57. Class 40 (4). In a loud-speaker having a horn-loaded high-frequency pressure unit mounted concentrically with respect to a low-frequency unit, the diaphragms 1, 3 of the two units being associated with the voice coils 2 and 4, respectively, in the annular air-gaps 14 and 15 between the ends of the central polepiece 7 and the centrally-apertured end-plates 9 and 10, which are spaced apart by the cylindrical magnet 11, rigid locating elements 16 and 17, each in the form of a dished ring, are interposed between the end portions 7a and 7b of the centre polepiece 7 and the centrally-apertured plates 9 and 10, respectively, to effect centring of the polepiece. Such a ring is shown in cross-section in Fig. 4, and may be pressed out from brass, aluminium or other non-ferrous metal, or moulded in plastic, or fashioned from wood. The ends 7a and 7b are turned down by machining to provide annular shoulders 18 and 19 which limit the inward axial sliding movement of the rings during assembly. The inner faces of the plates 9 and 10 are annularly rebated adjacent the apertures 12 and 13 to form annular shoulders 20 and 21 (at right-angles to shoulders 18 and 19) against which the flanges 16a and 17a contact on assembly. To allow for tolerances in manufacture in the length of the polepiece 7 and the magnet 11, these parts are deliberately dimensioned so as to provide an annular gap 24 between the ring 17 and the shoulder 19, which gap accommodates a compressible ring 25 of, for instance, neoprene. The inner end of the horn 5 is screwed into the end 7b of the centre polepiece 7. Centring of the voice coil 4 is achieved by adjustment of the grub-screws 28, in the lugs 27 provided on the chassis 23, which bear upon the periphery of the plate 10.