GB317641A - Improvements relating to electromagnetic sound reproducing devices - Google Patents

Abstract

317,641. Brandes, Ltd., and Hoban, M. S. Aug. 22, 1928. Magnetic instruments.-The actuating movement for a large-diaphragm loud-speaker or gramophone pick-up is of the balanced-armature type in which a polarizing magnet bears two parallel pole-pieces, disposed on either side of the magnet, and overlapping to form an air-gap in which an armature extending parallel to the gap is mounted so as to be capable of oscillating to and from the pole-pieces which carry operating coils. A horse-shoe magnet 1, Fig. 1, carries substantially F-shaped pole-pieces 2, 3, the stems of which are bolted to opposite sides of the magnet, while the branches 3a, 3b of the one project towards those of the other, both bearing coils 15 wound on formers 16. The armature 5, of highly permeable material, Fig. 3, consists of a rectangular portion 5 with an extension 10 bearing a driving rod 11, and two integral supporting members 6 terminating in portions 7 which are bolted to bridge-pieces 12, spanning the pole-pieces 2, 3 and bolted thereto. The natural frequency of vibration of the armature 5 may be modified by drilling holes 14 in the supporting members 6, and the pole-pieces 2, 3 may be laminated. The actuating fluxes, circulating through the armature and the bifurcated parts of the polepieces have very low reluctance paths. According to the first Provisional Specification the pole-pieces may be of U-shape and clamped to the limbs of a permanent magnet, the limbs of the pole-pieces projecting inwardly, and a coil being provided on each limb.