GB595739A - Improvements in or relating to electrodynamic loudspeakers or microphones - Google Patents

Abstract

595,739. Moving-coil instruments. TRUVOX ENGINEERING CO., Ltd., and WARD, L. R. May 28, 1945, No. 13342. [Class 40 (iv)] In a moving-coil microphone or loud-speaker, a single fixing member operating through the medium of a non-magnetic centring member serves to draw into position the whole of the magnetic structure together with a chassis supporting the diaphragm. In one embodiment, Figs. 1, 1a, the non-magnetic centring member 5 is swaged, brazed or rolled on to the top plate 4 and has a central hole into which a boss 3b on the upper part 3a of the central polepiece fits, but does not extend sufficiently far to project through it. The bolt 10 holds the whole assembly together including the outer conical chassis 8 gripped between the cylindrical magnet 1 and the top plate 4. The bottom plate 2 may be dished, Fig. 2 (not shown), so that the central polepiece consists of the bossed upper part only, the centring member being secured between it and the bottom plate. Instead, the bottom plate may be flat and the centring member correspondingly dished, Fig. 3 (not shown). The centre pole may be an independent member provided with a head 11, Fig. 5, fitting neatly in a hole in the bottom plate 2, the whole assembly being secured by the bolt 10. The centring member 5 is here provided with a turned-over outer edge which fits into a groove 12 in the top plate 4. The upper polepiece in this case is not provided with a boss, the centring member being a close fit over the lower polepiece 3. In Fig. 6 (not shown), the centring member is conical, its taper fitting a corresponding taper in the upper part of the central polepiece and split or slotted to make it springy and arranged so that on pressure from the conical polepiece it is sprung into a suitable groove in the top plate 4.