HAYES— DETECTION OF SUBMARINES. 



27 



each receiver of each group reaches its respective ear in phase, 

 thereby giving a maximum intensity for any sound travehng in a 

 direction perpendicular to the hne of receivers, as represented by 

 arrow i'. Moreover, the resultant sound at the two ears will be in 

 phase so the listener will hear the sound binaurally centered. Sounds 





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Plate X. Principles of M-B tube. 



from any other direction, such as represented by arrow 2', will not 

 reach the ears in phase and therefore will be weakened in intensity 

 in both ears. As represented, the composite sound reaching the left 

 ear will arrive in advance of that from the group of receivers con- 

 necting with the right ear. This weakened sound will therefore 

 not be binaurally centered but will appear to be located to the left 

 of the listener. Such sounds are often spoken of as being " out of 

 focus." 



The intensity of sounds " in focus " is directly proportional to 

 the number of receivers connecting with each ear. The intensity of 

 sounds out of focus depends upon the length of line, the spacing of 



