GB597935A - Improvements in or relating to moving coil loud speakers and other electrical devices having a member movable in a magnetic gap - Google Patents

Abstract

597,935. Microphones; loud-speakers. FOUNTAIN, Ltd., G. R., HOULGATE, H. J., and WHEELER, G. C. Nov. 16, 1944, No. 22654. [Class 40 (iv)] Electromagnetic apparatus having an annular coil movable in an annular magnetic gap formed between two concentric polepieces, comprises a coil-supporting holder which is detachable from the magnetic structure and is formed with portions of magnetic material fitting within the gap and engaging at least one of the pole faces of the magnetic structure to locate the holder with respect to the magnetic gap and means for supporting the coil from the holder with the coil located with respect to the portions of the holder which fit within the magnetic gap. As shown in Fig. 1, the diaphragm 3 having a flexible portion 3a and carrying the coil 1 is mounted between discs 4a held in a cup-shaped holder 4 having a flange 6 of magnetic material engaging the inner surface of the outer polepiece 7. A ring 9 secured to the polepiece 7 centralises the polepiece 8 within the gap. In a modification, Fig. 2, the cup-shaped member 4 is provided with a cap 10 fitting the centre polepiece 8, the flange 6 and the cap 10 being connected by an annular member 9 of non-magnetic material. The flange(s) of the holder may be discontinuous and comprise sections shaped to fit corresponding slots in the pole-face(s) of the magnetic gap. The polepiece 8 and the cap 10, Fig. 2, may be formed with an aperture for transmission of the sound from the diaphragm 3. If a cone diaphragm is employed the holder may be formed with struts to support the outer periphery of the diaphragm.