GB147939A - Improvements in submarine sound transmitting and receiving apparatus - Google Patents

Abstract

147,939. Signal Ges. March 10, 1917, [Convention date]. Subaqueous audible signals.-The diaphragm 1 in contact with the water is separated from the sound producing or detecting device by a flat gasfilled chamber 4 of very small volume. The invention is illustrated in connexion with receiving- apparatus of electro-magnetic type. In the arrangement shown in Fig. 1, the gas chamber 4 is contained between the large outer diaphragm 1 and the small inner diaphragm 3, and communicates through a controllable throttle passage 8 with a large chamber 10. The diaphragm 3 carries the armature 5 of the detecting magnet 6. The coupling between the diaphragms 1 and 3 is closer the smaller the volume of gas, and, if the throttle passage were blocked, would be closer for low frequencies than for high. The throttle passage, however, tends to release the pressure-pulsations in the chamber 4, and this tendency is greater the lower the frequency, so that the total result is to favour the transmission of a particular range of frequencies, and to discriminate against frequencies higher or lower. The throttle passage also has the advantage of equalizing the static pressure on the two sides of the diaphragm 3. The closeness of coupling may be varied by changing the size of the gas chamber, or the pressure of the gas, and means may be provided for controlling these adjustments, as well as that of the throttle passage, from a distance. The diaphragms 1 and 3 and the detector itself may have the same or different natural frequencies, or may be aperiodic, so that the receiver as a whole may have either one or two or more predominant frequencies. If the diaphragms 1 and 3 have different natural frequencies, their effective frequencies when coupled will depend on the closeness of the coupling, and can be varied by varying the coupling. The coupling may also be varied for the purpose of adjusting the damping relations, for example to balance the radiation damping effect of the diaphragm 1 and the detection damping effect of the diaphragm 3. The amplitude of vibration of the diaphragm 3 may be made greater or less than that of the diaphragm 1 by suitably proportioning their sizes. There may be two gas-chambers 4, 11, Fig. 2, contained between three diaphragms of progressively diminishing size. To diminish the loss of energy by gas-friction in the shallow peripheral portion a of the chamber 4, a gas of small internal friction, such as hydrogen or ammonia, may be employed; or the gas-chamber 17, Fig. 4, may be surrounded or backed by liquid 15, so that the radial movements due to the difference in size of the diaphragms 1 and 3 take place in the liquid and not in the gas. The invention is applicable to receivers of the microphone type and to transmitters.