Patent GB-578729-A (GB)
Title: Improvements in or relating to electrical systems for determining the direction of sound sources
IPC: G01S1/72
Filed: 1938-06-03
Abstract: 578,729. Locating sounds and like vibrations. CONDLIFFE, G. E., and CLARK, H. A. M. June 3, 1938, Nos. 16668, 17823, 21394 and 26479. [Class 118 (ii)] [Also in Group XL] A method of obtaining an indication of the direction of a source of acoustic or other vibrations consists in causing the output of a pair of detectors to interact so as to produce two further outputs containing the directional intelligence in a different form, the further outputs being used to provide audible or visible indication of the relationship between the postion of the detectors and the direction of the source of vibrations. The method may be used for locating the source of a sound in air, such as an aeroplane, or in water or solids, or of a source of modulated electromagnetic waves. Specification 394,325 is referred to. In the system shown in Fig. 1, sound from a source 1 impinges on two microphones 2, 3 the outputs of which are combined by transformers 5, 6. The windings of these transformers are so arranged that the outputs from the secondaries 7, 8 respectively, are constituted by half the sum of the outputs from the two transformers and half the difference. Thus the output from the secondary 7 represents the average sound intensity at the two microphones, and the output from the secondary 8 has a value which depends on the angle of the incoming sound relatively to the plane of the microphones. After amplification in amplifiers 9 and 10, the signals are passed through attenuators 11, 12 and then through double wound transformers 13, 14 which supply to headphones 15 signals that represent the sum and difference of the signals from the amplifiers 9, 10. The attenuator 12 is made adjustable to control the amplitude of the signals in the difference channel relatively to those in the sum channel and to enable the effective spacing of the microphones to be adjusted. The headphones and the transformers 13, 14 may be replaced by a cathode ray tube 17, as in Fig. 3, the sum and difference channels being connected to the deflector plates of the tube. In this case, the attenuator 12 employs a shunt condenser 18 instead of a resistance, and the value thereof, and of the shunt resistance 19 in the attenuator 11, may be arranged to give any degree of amplitude difference for a given phase of sound inputs at the microphones. The microphones may be placed in individual rejectors or, as shown in Fig. 3, mounted symmetrically within a single reflector R, a further pair of corrective networks 20, 21 being included in the circuits. A group of two pairs of microphones may be used in conjunction with the reflector, each pair being so connected that vertical and horizontal bearings may be observed, the reflector being movable in any direction. The circuits may be arranged, also, so that both headphones and a cathode ray tube are included and may be used separately or together. A direct indication of the true bearing of a source of sound may be obtained by arranging four pressure microphones at the corners of a square the diagonals of which lie in northsouth and east-west directions. The outputs from opposite microphones are applied by networks of the kind described to the plates of a cathode ray tube, the line traced on the screen giving a true bearing of the sound source. This arrangement is of use for first observing rapidly the approach of an aeroplane as it does not necessitate searching with the microphones. Instead of using pressure microphones, velocity microphones, using a longer and heavier ribbon than usual, may be used. In all arrangements, the cathode ray tube may have its fluorescent screen arranged at the centre of a large scale map covering the range of the apparatus. Other forms of visual indicators may be used, and resistance networks connected in the manner of a Wheatstone Bridge may be employed to provide the sum and difference outputs. Further, instead of using the sum of the outputs of the two detectors in a pair, the output from an additional single detector may be used. Instead of microphones, any suitable form of detector capable of transforming acoustic into electric energy, such as a piezo-electric device, may be used.