Patent GB-146193-A (GB)
Title: Improvements in or relating to the directive reception of sound or other wave energy
IPC: G01S1/72
Filed: 1920-06-25
Abstract: 146,193. Steward Davit & Equipment Corporation, (Assignees of Pierce, G. W.). June 25, 1919, [Convention date]. Locating subaqueous sounds.-An electric compensator, comprising time-lag circuits, is employed for adjusting the phase of currents from two or more receivers such as microphones. The invention is described with special reference to determining the direction of sounds. The cornpensator can be used for bringing into phase the currents transmitted by two microphones to two separate telephones, to enable the direction of a sound to be determined by the binaural sense ; or for adding the effects of a large number of microphones in phase as regards sounds arriving from a given direction, while sounds from any other direction give interfering components and a weaker resultant; or both methods may be used in combination. The time-lag circuits comprise a number of inductances in series and capacities in shunt; each section, consisting of an inductance and capacity, introduces a definite amount of retardation, and a variable number of sections can be cut into circuit. In the binaural installation shown in Fig. 2, microphones 31, 32 are separately connected to telephones 33, 34 through transformers 35, 36 and the left-hand and right-hand portions of a time-lag circuit 37 - - 41. Tho relative retardation of the two circuits is controlled by a switch consisting of a row of conducting blocks 56 - - 75 movable under pairs of brushes 44, 45, &c. In the position shown, sections 37 and 38 of the time-lag circuit are in series with telephone 33 and section 41 in series with telephone 34; sections 39 and 40 are short-circuited by the L-shaped blocks 65, 66. If the blocks are moved one step to the left, the number of sections in series with tele. phone 33 is unaltered but an additional section is introduced in the circuit of telephone 34; a further step to the left leaves unaltered the numher of sections in series with telephone 34 but withdraws a section from the circuit of telephone 33; and so on. When the switch is adjusted so that the sound reaches the two ears in phase the sound appears to the listener to he binaurally centred, and movement of the switch in one or other direction makes the sound appear to move to left or right of his head. The setting of the switch to produce this effect indicates the direction of the sound relatively to the line joining the microphones 31, 32. In practice, the circuit 37 - - 41 comprises a larger number of sections, and the switch-blocks 56 - - 75 are mounted in a circle on a rotary disk, with slipring connexions to the telephones, and with a scale to indicate the direction of the sound. Fig. 5 shows compensating-circuits for a row of twelve microphones, which may be mounted along a ship's side. There may be twelve microphones on each side of the ship, with means for switching the compensator into circuit with either the port or starboard set. The secondaries of the microphone transformers are connected between leads 401 - - 412 and a common return 413. The microphone circuits are branched in groups of three; for example, the circuits 401, 403, 402 are connected to the junction 531 through the left and right portions of the time-lag circuit 501 and through the timelag circuit 502. When the switch 521 is at the centre of the circuit 501 the retardation in these three branches is the same, but by adjusting the switch 521 the retardation can be made progressively greater or less from each branch to the next, so that the currents generated in the microphones 401, 402, 403 can be brought into phase at the junction 531 for any given direction of the sound. By similar adjustment of a switch 522 the currents from microphones 404, 405, 406 are brought into phase at junction 532, and the currents from junctions 531, 532 are brought into phase at junction 631 by adjusting switch 621 on circuit 601. Similarly, the currents from microphones 407 - - 412 are brought into phase at junction 632, and finally the currents from junctions 631, 632 (i.e. from the first six microphones and from the other six) are brought into phase by a switch 701, similar to that shown in Fig. 2, and delivered separately to the telephones 803, 804. The compensator switches are constructed in rotary form and are all operated by the same shaft, so that a single movement sets the compensation for sounds from any given direction, as indicated by a scale. The correct setting of the compensator is that which makes the sound appear of maximum intensity and binaurally centred. By closing a switch 810, so as to put the two telephones in parallel, the binaural effect can be cut ont, direction being judged entirely by intensity. If the binaural effect is left out of account, as in the application of the invention to wireless telegraphy, the final element 701 of the compensator mav be of the same simple form as the element 601. The Specification gives directions for calculating the inductance and capacity necessary to produce a given time-retardation per section of the timelag circuits; for calculating the attenuation of the current in a series of sections; and for proportioning the elements of the circuits so that a maximum part of the energy of the microphones is delivered to the telephones, with a minimum of reflexion at the various junction-points. In order that the retardation may be the same for all frequencies present, the retardation introduced by each section of the time-lag circuits should be as small as is conveniently possible.