![]() ![]() these were due to the acoustic properties of the earpiece, mismatching at the diaphragm/water interface and reflexions and absorptions in the tank itself. Preliminary tests with a calibrated hydrophone in metal tanks rather smaller than those at Naples had shown that many resonances occurred over the range 50-30,000 cyc./sec. The audio-oscillator was connected to the earpiece through a shorting key which was opened during the period required for the sound stimulus for reasons which will be discussed later no attempt was made to limit the transients in the diaphragm at the beginning and end of the stimulus. 2 shows a block diagram of the electrical apparatus. This material will allow the release of at least twentyįig. greater than that of the earpiece was made from cold-curing silicone rubber (Midland Silicones Ltd. ![]() ( c) A hollow cylindrical mould whose diameter was about 1 cm. The twin wires were connected to the telephone terminals and the screening connected to one of them. back from the face of the hexagon head and the emergent twin wires and the screening were sealed in with ‘Araldite’ adhesive the exit of the cable at the other end of the bolt was also sealed. The outer covering was arranged to lie about 3 mm. long, was drilled axially so as to allow a screened twin-core, P.V.C.-covered cable to be threaded through with a tight fit. ( b) A hexagonal-headed brass bolt, 12 mm. ( a) The diaphragm-retaining ring was removed so as to present the maximum vibrational area to the water, and the diaphragm itself was sealed with ‘Araldite’ adhesive to the earpiece all round its outer edge all screw heads in the surface of the earpiece were also sealed and filled with the same material. ![]()
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