GB747023A - Improvements in or relating to electro-acoustic transducers - Google Patents

Abstract

747,023. Electroacoustic transducers. WARNER, H. C. Aug. 4, 1953, No. 21510/53. Class 40(4). An instrument such as a pick-up or microphone in which the resistance between electrodes in a fluid medium is varied in accordance with mechanical vibrations comprises three chambers each containing an electrode and filled with fluid and means is provided for varying in opposite senses the size of orifices connecting the central chamber with the outside chambers. In a pickup, Figs. 1, 5, 8, chambers 12, 13, 16 formed in a block 11 and filled with electrolyte are closed at their lower ends by a flexible diaphragm 17 of soft rubber or latex, and the stylus 30 carried by a supporting member 36 having a raised rim holding the diaphragm against the cylindrical wall of the central chamber serves to flex the diaphragm as in Fig. 8 to vary the size of the inter-electrode path through the electrolyte. The supporting member is held in yielding engagement with the diaphragm by means of a soft rubber cushion 39. The tension is adjusted to give a linear change of orifice when plotted against needle deflection and the differential arrangement renders it suitable for connection to a push-pull amplifier as in Fig. 10 (not shown). Connections to a single valve amplifier are also described. The electrodes may comprise a thin metal lining or a metallic deposit on the walls of the chambers. The electrolyte may be a solution of cadmium sulphate in ethyl alcohol with cadmium electrodes, or a solution of alum in ethylene glycol with electrodes of a nickelsilver alloy. A conductive gas such as argon or neon may also be used. An alternative embodiment having three parallel chambers cut lengthwise in a block and having the working diaphragm across the top is described with reference to Figs. 11-22 (not shown), the electrodes being embedded in the block and running the length of their respective chambers. The stylus holder is in this case extended in the form of a crucifix across the top of the diaphragm. A similar unit, Fig. 25, forming part of a microphone, may be actuated by a diaphragm 105, Fig. 26, which is dimpled or corrugated for additional stiffness and attached by supporting vanes to the cross-piece 113. Springs 117 hold down sponge rubber pads 118 so that the gap between the chambers is limited to an area in the vicinity of the cross-piece 113. A further embodiment in which a number of rows, each of three chambers, have their electrodes interconnected to give an additive effect is described with reference to Figs. 27-30 (not shown). The use of such a variable-resistance instrument as an amplitude or phase modulator and as a sub-aqueous signalling unit is also mentioned.