Description
Physical description
locator
The Sound Locator consists of 4 wooden trumpets and 2 stethoscopes, mounted on a wooden support and a tripod.
History note
Original caption:
"Sound Locator No1 Mk1
For use with anti-aircraft sections and designed for detecting the direction of the sound made by aircraft audible but invisible from the ground, and for indicating the angle of elevation and bearing in azimuth of such aircraft, thus enabling them to be more readily picked up at night by searchlights.
It consists principally of four wooden trumpets, a wooden support, a tripod, two stethoscopes, and an azimuth scale plate.
The trumpets and stethoscopes are mounted on pivots which allow of movements in elevation and azimuth. Two of the trumpets were for obtaining the direction in elevation and two for obtaining it in azimuth.
An azimuth scale graduated in single degrees to 360 degrees, an angle-of-sight scale graduated in single degrees to 90 degrees, and an open sight are provided. The searchlight beam was kept in contact with the edge of this ring sight by a layer, who gave the necessary directions to the men at the projector.
The locator can be leveled by means of a cased spirit bubble No1, which is mounted immediately above the vertical spindle.
The results obtained were not very satisfactory owing to the fact that little was known about the vagaries of the paths of sound waves in the atmosphere and the impossibility of eliminating other similar sounds on the ground in the neighborhood of the locator"
Other information:
This design of Sound Locator obtained a maximum accuracy of 1/10 of a degree, compared to human ears which give about 5 degrees.
At least nine marks of Sound Locator were produced and improved forms of this instrument were still in use in 1939-1940, before being superseded by radar.
Extract from Canadian War Museum website:
The Mk 1 Sound Locator was manufactured by A.W. Gamage Ltd. in Britain during the first World War. In the early days of the First World War, anti-aircraft defence was a totally new field. The detection of unseen incoming aircraft was a major problem. The only possible solution with the technology available at the time was sound detectors, which could provide a rough idea of an aircraft's direction and height based upon the sound of its engine. Tubes connected the bases of two horizontally mounted gramophone-style horns to a pair of stethoscope earpieces. An operator moved the detector until the sound was heard equally in each ear, at which point (theoretically) it would be pointed in the direction of the aircraft. A second operator used the vertically mounted horns to estimate height. The system was rudimentary at best, however, as the location of the aircraft could only be established for the time that the sound was recorded. After a sound contact was made, laborious calculations were then required to properly aim an anti-aircraft gun, and any deviation in the aircraft's flight path rendered the system useless. It was, however, the only system available for detecting the approach of unseen aircraft until the development of radar in the 1930s.