GB833406A - Improvements relating to moving coil loudspeakers and similar transducers - Google Patents

Abstract

833,406. Loud-speakers. TANNOY Ltd. March 21, 1958 [Jan. 4, 1957], No. 9154/58. Divided out of 465/57. Class 40 (4). The moving parts of a moving-coil loudspeaker are enclosed in a flameproof casing 10, the diaphragm 25 being adjacent a group of flameproof openings 27 in a relatively thick front assembly 28 through which the sound is emitted. As shown the central polepiece 2 is mounted on the permanent magnet slug 4 which is secured to the back plate 5 by screw 6, the remainder of the magnetic circuit consisting of an outer polepiece 3 and a cylindrical part 7, the space between part 7 and the slug 4 being filled with inert material. The fireproof casing 10 consists of a casting 11 fitted with a removable front plate 12. The openings 27 are constituted by a number of concentric annular slits formed between concentric tubes 30, the assembly of tubes being mounted within a circular opening in the front assembly 28 while the central space is filled by a plug 31. The tubes are located by thin spacers (not shown). Each opening 27 is approximately sixteen thousandths of an inch wide and the narrow width in combination with the relatively high thermal capacity provided by the thickness of the assembly 28 and the plug 31 renders these openings flameproof. A normal type of reentrant horn is fitted. The flameproof casing 10 also encloses a transformer 15 the secondary winding of which is connected to the speech coil 1 by conductor 16, and the primary winding of which is supplied through conductor 17 connected to a bolt 18 passing through an insulating bush 19 in the wall of an auxiliary chamber 20 fitted with a rear plate 21. Connection to the chamber 20 from outside the casing is made by way of a flameproof gland 22.