Patent GB-162034-A (GB)
Title: Improvements in or relating to sound detecting systems
IPC: G01S1/72
Filed: 1920-01-09
Abstract: 162,034. Graham, E. A., and Rickets, W. J. Jan. 9, 1920. Locating sounds; receiving and detecting audible signals.-In apparatus for detecting and locating the source of sound transmitted through the ground or through water, as in submarine signalling, electromagnetic means are provided whereby the detecting microphone is shaken, to maintain sensitiveness, whenever the apparatus is switched into use, and whereby the microphone can be vibrated at will with audible frequency for testing purposes. Two detectors are used for locating purposes, for example at opposite sides of a ship, and switching arrangements are provided so that a telephone head-piece may be connected to either detector at will, rapid changeover being possible for facilitating comparison of intensities of effects in the two detectors, without a disturbing " click " in the telephone receiver when the change is made. The two detectors may also be used binaurally, and unwanted sounds may be eliminated by the use of a tuned circuit and three-electrode amplifier. The detecting device M comprises a casing 1, the wall 1<c>, which serves as a diaphragm having a projection 1<b> adjustably pressed against the ship's plating 2 by screws 3. Within the casing a three-armed lever is pivotally mounted on the wall 1<c>, the arm 5a being held against the wall by a spring 5d bearing against the arm 5<c>. The third arm 5b carries an inertia-type microphone 9. A chamber containing desiccating material 10 may be provided. The arm 5a acts as the armature of an electromagnet 6 by which it can be attracted' and released to agitate the granules in the microphone, or can be given a comparatively feeble oscillation to produce microphonic current variations of audible frequency for testing purposes. The wall 1<c> may be a separately formed tuned diaphragm, or its place may be taken by the plating of the ship. The second detector M<1>, shown diagrammatically, is also constructed as above described. The detectors M, M<1> and a telephone headpiece H are connected to a switchboard within the casing of which, in addition to the necessary contact devices and connections, may conveniently be disposed inductances 17, 17a for connection with the microphones at M, M<1> respectively, a vibrator 15, and a condenser 14 in series with the head-piece H. The contacts are controlled by a cam 12b operated by a switcharm 12a external to the casing, and having an indicator 12<c> as shown adapted to show through an opening. Normally, the switch arm and cam are held in the " off " position at X by a spring 19 As the arm 12<a> is moved to the position Y, the cam 12b first closes contacts 12<d>, 12<e> and supplies currents to both magnets 6. The cam then allows these contacts to open, de-energizing the magnets and shaking the microphones, and allows contacts 12d, 12f, supplying current to both microphones, to close. At the same time contacts 12<g>, 12<h> are allowed to close, connecting the head-piece H and condenser 14 across inductance 17, so that disturbances affecting detector M are heard. Further movement of the arm 12<a> to position Z maintains the microphone circuits closed, but breaks contact between 12<g>, 12<h>, and closes contacts 12<g>, 12i, connecting the headpiece and condenser across inductance 17<a> connected to detector M<1>. By moving the arm 12a backwards and forwards between positions Y, Z, the disturbances affecting detectors M, M' are heard alternately, rapid movement facilitating comparison of intensity of disturbance in the two detectors to enable direction of the sound source to be estimated. As the microphone circuits remain unbroken, and no direct current flows through the head-piece H, no disturbing " click " is heard as the change-over is made. In an alternative arrangement, the speed of change-over is made independent of the rate at which the arm 12a is moved, the movement of the change-over contact being effected by an electromagnet, the circuit of which is controlled by the cam 12b. A modified arrangement is also described whereby the two detectors may be compared, as above, or used simultaneously and binaurally, to estimate the direction of the source of sound. Depression of a press-button 13 closes contacts so that current is supplied from a battery through resistance 16a, vibrator 15, and resistance 16 in series, and at the same time resistance 16 is bridged across both magnets 6 so that both microphones are agitated with frequency depending on that of the vibrator. The effect on one microphone or the other can be heard in the head-piece H, according to the position of switch-arm 12a. To eliminate disturbing frequencies, the head-piece If may be connected to the plate circuit of a three-electrode amplifier 26, Fig. 8, the grid circuit of which includes a coil 21, inductance 22 adjustable to tune the circuit to the required frequency, and a shunt condenser 23. The coil 21 is inductively coupled to a coil 20 which can be connected to either detector M, M<1>.