6 HAYES— DETECTION OF SUBMARINES. 



sound is lost and, as has been stated, it is the quahty of a sound 

 that enables the listener to name the instrument on which it is pro- 

 duced. Secondly, resonant receivers do not faithfully reproduce 

 phase and therefore are not well suited for use with devices operat- 

 ing on the binaural principle or which employ multiple receivers. 



In this country emphasis has been laid on the development of 

 non-resonant receivers. Such receivers are of the pressure type and 

 though they are not so sensitive as the resonant type, and as a result 

 can not give as great range when entirely free from disturbing 

 noises, yet they do give a faithful reproduction of the sound thus 

 making it possible for a trained listener to distinguish a submarine 

 from other boats or water noises or noise from his own engines by 

 the quality of the sound. Such receivers are suitable for use in bi- 

 naural and multiple unit devices. 



These receivers consist of a flexible chamber or a rigid chamber 

 carrying a flexible diaphragm, preferably rubber. Since the volume 

 of the receiver changes readily under variation of hydrostatic pres- 

 sure, the water in the neighborhood of the receiver will be subject to 

 less or greater pressure than at other points in the wave front, de- 

 pending upon whether the volume change in the receiver is positive 

 or negative. In order to establish pressure equilibrium the particles 

 of the highly incompressible medium will be forced toward or from 

 the receiver for a considerable distance beyond its surface. The re- 

 ceiver therefore absorbs the sound energy from a comparatively 

 large volume of water which fact accounts for its rather high 

 sensitivity. 



Types of Submarine Receivers. 



Five types of submarine receivers have thus far been developed. 

 Plate I shows the principle of each of these five types. 



The Acoustic Receiver consists of a flexible chamber connected 

 through a tube to the ear. The walls of the chamber are made of 

 rubber or thin metal. 



The Geophone consists of two metallic plates between which is 

 compressed a flexible rubber ring. The upper plate is made massive 

 to give it inertia while the lower one is made lighter in order that its 

 inertia may not seriously interfere with its motion. The intervening 

 air space connects by tube through the inert plate to the ear. Such a 



