GB995744A - Improvements in electromagnetic electroacoustic transducers - Google Patents

Abstract

995,744. Transducers. R. GORIKE. Nov. 24, 1961 [Nov. 30, 1960], No. 42219/61. Heading H4J. An electric acoustic transducer comprises a central permanent magnet 1, having polepieces 2, 3 defining an air gap 5, and a ring armature 4 of greater diameter than the polepieces, the ring engaging a non-magnetic armature support at its inner edge and being connected at its outer edge to a diaphragm 6. The exciter winding 7 is concentric with the axis of the permanent magnet. As shown, the pole pieces are flat and pot-shaped respectively but two pot-shaped polepieces may be used, the magnetic and coil systems being symmetrical about the armature, Fig. 5 (not shown). The non-magnetic support 9 may lie in a further air gap between an inner annular ring and the flat polepiece, the inner annular ring being formed from a further pot-shaped piece within the first mentioned pot, Fig. 2 (not shown) or alternatively the polepiece 1 may be flat and provided with a circular magnetic member of U-shaped cross-section the limbs of the U and the polepiece 2 providing two gaps, one for accommodating the outer moving edge of the armature and the other accommodating its fixed inner edge, Fig. 3 (not shown). Alternatively, the polepieces may themselves comprise two cylindrical portions integral with a flat circular portion, Figs. 6, 7 (not shown). In arrangements in which a free space is provided around the permanent magnet bore-holes in the polepieces may be provided to connect this space with the air space behind the diaphragm and with the open air, Fig. 6 (not shown). Fig. 8 illustrates a complete embodiment in which the permanent magnet 1 is perforated and contains a hollow rivet 15 for holding the polepieces 2, 3. The diaphragm has a corrugated rim zone 17 via which it is mounted on the casing 19. Member 21 defines a shallow space behind the diaphragm, which is connected to the larger space 26 inside the casing by holes 24 covered with damping material. Damping material is also provided in the hollow rivet. The space 26 communicates with the open air via a tube 27. Bore holes in the polepieces may also be provided as described above. The diaphragm 4 may be slit as shown, Fig. 4, at 11 or 13 to provide greater resilience. It may also be provided with additional magnetic material towards its outer edge, by the addition of a circular ring riveted or stuck thereto.