GB803283A - Improvements in or relating to electroacoustic transducers - Google Patents

Abstract

803,283. Loud-speakers. BAERMANN, M. Oct. 17, 1955 [Oct. 28, 1954], No. 29603/55. Class 40 (4). In an electro-acoustic transducer, a perinanent magnet attached to the mechanicallyvibrating elements is disposed in an air gap formed by the parallel pole faces of an electro magnetic circuit so that it is free to vibrate ina direction at right angles to the gap field, and is magnetized at right angles to the direction of motion. The permanent magnet is mounted to have a. position of rest displaced from the centre of the gap field and may be a bar magnet magnetized transversely of its length or annular with radial magnetization. A number of bar magnets in parallel gaps may act simultaneously on the same diaphragm of a loud-speaker or microphone. In the loudspeaker, Fig. 2, two annular magnets 4, 5, joined by a ring of polystyrene, are mounted and spaced to overhang the pole faces and are magnetized in opposite directions. The coil 2 may be connected directly in the anode circuit of an output valve and the effect of the D.C. component is counteracted by a magnet 11 and an adjustable shurit 12. A further modification in which two magnetic circuits act simultaneously on a single permanent magnet is described with reference to Fig. 3 (not shown).