GB926277A - Full range electroacoustic transducers - Google Patents

Abstract

926,277. Loud-speakers. BOYEN & RICH Inc. July 3, 1961 [July 18, 1960], No. 23983/61. Class 40 (4). In a moving coil electroacoustic transducer a substantially sheet form of magnetic flux extends over a prescribed area from a pole adjacent the middle of the area to a second pole around the periphery of the area and a diaphragm extends over the said area and carries a continuous flat spiral coil over substantially the whole area between the poles so that an alternating current in the coil will produce mainly isophasal motion of the whole of the diaphragm. Fig. 1 shows a transducer in which a sheet of magnetic flux is produced between an annular polepiece 21 and a magnet 11 mounted in the centre thereof, two similar units being mounted with a diaphragm 31, Fig. 2, clamped therebetween to be in the same plane as the magnetic flux sheet between the opposed N poles of magnets 11 and 12 and the annular polepieces. A flat spiral coil 32 is mounted on the diaphragm and extends into the area between the opposed magnets so that substantially the whole of the diaphragm is active. It is suggested that the outer polepieces and the magnet might be circular, Fig. 8, not shown. Diaphragm construction.-The diaphragm may be a sheet of nylon fabric or a thin sheet of suitable plastic or aluminium foil having the coil cemented to its surface by a permanently non-rigid cement if a hard material, e.g. polyester film, is used a damping material, e.g. woven nylon mesh, polyfibrous paper, or a plasticized film material, may be applied to the diaphragm to absorb flexural vibrations. In an alternative form the diaphragms may be mounted via a compliance rim 42, Fig. 10, of, e.g., rubber and, in addition, to enhance the frequency response the diaphragm may be loaded by a copper ring 51, Fig. 12, mounted around the periphery and the diaphragm stiffened and loaded by bars 52. Specification 193,339 is referred to.