GB282279A - Improvements in electromagnetic speaker units - Google Patents

Abstract

282,279. Waddell, B. F. May 14, 1927. Magnetic instruments.- An electromagnetic unit for a loud-speaker comprises a permanent magnet and co-operating armature with means for balancing the armature in the air gap between the magnet poles, means for completing the electromagnetic circuit through the armature. and a fixed means of leakage of magnetic flux across the poles of the permanent magnet the armature being supported near one end thereof bv this fixed means, which serves also to amplify the electromagnetic flux in the armature. The fixed means preferably consists of a reed of magnetic material. In the construction shown, a yoke 2 of non-magnetic material is secured across the terminals of a horseshoe magnet 1 with metal spacing blocks 4 of high permeability in between. The yoke is curved at the centre, providing a circular receptacle, the walls of which are extended laterally to form lugs 6, on which is clamped a non-magnetic bar 7, which retains the speech-current coil 9 in the receptacle. A reed 10 of magnetic material is secured by screws 11 to the lugs 6, an armature 16 being secured near one of its ends to the centre of the reed and passing through the coil 9, so that its other end lies between the ends of pole shoes 12 secured by screws 13 to the blocks 4 and by screws 14 to the lugs 6. The screws 11, 14 are of iron and preferably abut, although a slight air-gap may be left between their adjacent ends. A rod 17 connects the armature with a diaphragm, preferably of the form described in Specification 297,131. A leakage of permanent magnetism occurs from one magnet pole to the other through the screws 14, 11 and reed 10. whilst the electromagnetic circuit is completed through the armature 16, reed 10, screws 11, 14, pole-shoes 12, and air-gaps. When the telephonic current produces magnetic flux in one direction, the armature moves to reduce one air-gap and at the same time picks up some of the permanent magnetism of the correct polarity from the reed, thus amplifying the magnetic flux in the armature, i.e. some of the magnetism which was flowing straight across the reed is now deviated to a path through the armature and the reduced air-gap. In a modified construction, the reed 10 is extended to the outer sides of the magnet 1, its outer ends being clamped to the blocks 4 by screws having the same relation to the screws 13 as the screws 11 have to the screws 14.