HAYES— DETECTION OF SUBMARINES. 



39 



The statement that no increase in range is to be gained by increas- 

 ing the sensitiveness of the receivers beyond a certain point ob- 

 viously does not apply when the receivers are used in multiple since 

 the local and other disturbing noises are not intensified in the same 

 proportion as the sound upon which the receivers are focused. More 

 sensitive receivers can be effectively employed in multiple unit de- 

 vices than in single unit devices such as the " 3-spot " and " 4-spot." 



The sensitiveness of the acoustical receivers is not as high as can 



A 



B 



Plate XV. The microphone housing developed at the U. S. Naval Ex- 

 perimental Station. A, Section through interior showing microphone. B, 

 Complete receiver unit, about ^ natural size. 



be advantageously used in multiple unit devices. This fact, together 

 with the need for a long range listening device led to the develop- 

 ment of several types of electrical listening devices employing mul- 

 tiple receivers. A description of these devices follows : 



The U-3 Tube is a submarine sound-detecting device which can 



