GB600853A - Improvements in and relating to transducers for radiating and/or receiving vibrational energy - Google Patents

Abstract

600,853. Diaphragms. BRUSH DEVELOPMENT CO. Aug. 14, 1945, No. 20952. Convention date, June 2, 1944. [Class 40 (iv)] [Also in Group XL (c)] In an electro-acoustic transmitter or receiver for use in air or a liquid medium, different regions of the radiating or receiving surface have different amplitudes and areas, so that the maximum effect may be along the axis. Thus, a circular diaphragm 13, Fig. 2, may be surrounded by an annular diaphragm 14, their amplitudes being in the ratio 2.4 : 1 and their radii in the ratio 0.607: 1, so as to minimize the side lobes of the polar response pattern. Alternatively, Fig. 4 (not shown), there may be three circular zones, and the Specification shows how to calculate the requisite areas and amplitudes. In a loud-speaker which approximates to these conditions, Fig. 7, the radiating surface is formed by piezoelectric crystals of the expander type, made of Rochelle salt, primary ammonium phosphate, or the like and energized along the electric axis (which is transverse in Fig. 7 so that the crystals expand in a direction normal to the plane of the Figure). The difference of amplitude may be obtained by applying the same voltage to all the crystals, but making the crystals in the inner zone 45 thinner between the electrodes than those in the outer ?,one 46, so that they have a larger voltage - gradient. Alternatively, different voltages may be applied to crystals of equal size, Fig. 5 (not shown), the difference being produced by series-parallel grouping, Fig. 12 (not shown), or by the use of different amplifiers, or the crystals may differ in length, Fig. 6 (not shown). The crystals are mounted on a heavy glass base 41, Fig. 8, so that wide margins around the electrodes are unnecessary, and sound-proof pads 40, 39, of rubber-impregnated cork, corprene or the like, are provided inside and outside the housing 35. The crystals are separated by corprene or the like, as described in Specifications 600,248 and 600,300, and may be mounted in strips, adjacent crystals having opposite polarities ; they are ground flat as an assembly. A rubber cover 38 is provided, and the housing is filled with glycerine through the opening 49. In another embodiment, Figs. 9, 10, 11 (not shown), the vibrating surface and its zones are rectangular instead of approximately circular. The directional radiation pattern may be varied by variously connecting eight such zones, and the housing may contain an amplifier.