Recorder, Sound Ranging, No.1 Marks II, III and IV


The Recorder S.R. No.1, Mk II is designed to record the respective times of arrival of a sound wave at a set of surveyed points, generally six, each occupied by a microphone. The record is made photographically by means of an electrical impulse conveyed from each microphone either by line wire or by a "Radio Link S.R".

At the recorder these electrical impulses are led to separate "strings" of a six-string Einthoven galvanometer. The resulting deflections of these strings are recorded photographically on a moving paper strip, generally referred to as the "film". Upon this film is simultaneously superimposed a scale of time marks, accurate  in rate but otherwise arbitrary, derived through a synchronous motor from the vibrations of an electrically maintained tuning fork. The unit of time is the "sound metre"which is the time taken by sound to travel one metre in conditions of still air of 50 per cent humidity at a temperature of 50dgr Fahrenheit. Development and fixation of the photo-sensitive film is automatic and the times of arrival of the sound at the several microphones can been read off as soon as the film leaves the fixing bath.