GB369030A - Loud speaker - Google Patents

Abstract

369,030. Loud-speakers. MAGNAVOX CO., 155, East Ohio Street, Chicago, U.S.A. April 15, 1931, No. 11145. Convention date, May 6, 1930. [Class 40 (iv).] A moving coil loudspeaker has its conical diaphragm 17 and coil 16 enclosed within a two - part magnetic structure comprising (a) a flat member 10 formed with spokes 11 to which is secured a central polepiece 12 adapted to project through the apex of cone 17 and (b) a conical frame member 13 secured at its periphery by screws 20 to the member 10 and having at its apex a flattened portion 14 to which is secured an annular polepiece 15 which co-operates with the central pole 12. The spokes 11, which are reduced in width so as not to interfere materially with the propagation of sound, have additional members 26 secured thereto and an energizing coil 24 surrounds the polepiece 12. Centring means 21 for the coil 16 is carried on the inner side of polepiece 15 to the outer surface of which is secured a non-magnetic pole centring device 22 adapted to engage a projection 23 on polepiece 12. The periphery of cone 17 is mounted on a flexible skiver 18 located between felt or cardboard washers 19, the whole being clamped between the members 10, 13 by the screws 20. Fig. 4 shows a modified form of pole centring device comprising a non-magnetic member 29 which is provided with a depressed portion 30 which engages the central pole 12 at a point substantially in line with the face of the outer polepiece 15 and is secured to polepiece 12 by a screw 31.