HAYES— DETECTION OF SUBMARINES. H 



It is evident that the difference in time of reception at the two 

 ears varies most rapidly, as the head is turned from a direction nor- 

 mal to a line joining the two ears and for this reason the listener can 

 judge this direction with greatest accuracy. 



This so-called " binaural principle " for determining the direction 

 of sound is not new. It has been used for determining the direction 

 of sounds in air, and was early recognized and tested by the British 

 for determining the direction of sounds in water. These tests were 

 unsatisfactory mostly for the reason that the apparatus was not 

 properly designed. All the listening devices developed in this coun- 

 try make use of this principle for determining direction. 



The direction of a submarine sound can be readily determined if 

 two like receivers (one connected to each ear of the listener) are 

 attached to a horizontal arm which can be rotated about a vertical 

 axis. In general, sound will not strike both receivers simultaneously 

 and as a result the impulses will not reach the listener's ears at the 

 same instant. Suppose the sound impulse reaches the listener's right 

 ear first, then the sound will appear to come from the right in ac- 

 cordance with the binaural sense, and if the path by which the sound 

 travels from the submarine receiver to the ear is the same for both 

 receivers, it must follow that the direction of the sound source is 

 along a perpendicular to the arm carrying the two receivers when 

 this arm is so oriented that the impulses reach the two ears in phase. 



A consideration of Fig. 2, Plate II., shows that the sound would 

 appear to be centered, were it coming from the direction given by 

 either of the arrows i or 2. This ambiguity in direction of 180 

 degrees can be removed by rotating the two receivers from the posi- 

 tion marked L and R to the position marked L' and R' . Let us sup- 

 pose that the receiver marked R attaches to the right ear and the one 

 lettered L attaches to the left ear. With the receivers in this second 

 position, if the sound comes from the direction given by arrow i, it 

 would appear to the listener to come from his right since it would 

 reach the right ear first. If, however, the sound should come from 

 the direction marked by arrow 2, it would appear to the listener to 

 come from his left since it would reach his left ear first. The am- 

 biguity in direction can therefore be removed by rotating the re- 

 ceivers somewhat from the position in which the sound appears to be 



