382 HAYES— U. S. NAVY MV TYPE OF HYDROPHONE. 



make the sound appear centered in the listener's head. It has been 

 found in practice that the average listener can determine the path 

 difference in water to within about one half inch. 



B/naum/ Arm AB'C 

 CompensofJon c/'Cco3 

 ^rror /nCbmpen.sat/cir> t S 

 frror /nAng/e a(?-'(?Co3'-^ 



ERROR IN ANCLE 'O'DUETO ERROR IN CDMPENSATnR SETTING 



Fig. 6. 



Referring to Fig. 6, it will be seen that this error due to the per- 

 sonal element may introduce a relatively large error in the determi- 

 nation of 9 and hence the same error in the sounding angle $ which 

 is the supplement of 6. 



For simplicity assume the hydrophone to consist of two single 

 receivers {A) and {B), Fig. 6, one connecting with each ear and 

 separated a fixed distance (C). Sound approaching from the direc- 

 tion represented by vector {V) makes an angle 6 with the line joining 

 the two receivers. The operator determines this angle by measuring 

 the distance {d) to within one half inch. Calling this error 8 we 

 have the following relation 



= cos"^ 



"c ■ 



The accuracy with which this equation determines 6 is propor- 

 tional to (C), the distance between the two receivers, and varies 

 with the value of {d). Since the value of the cosine changes slowly 

 with change of angle as the value of the angle approaches zero, it 

 is evident that the value of 8 will produce an abnormally large error 

 in the determination of 6 when the direction of the sound approaches 

 parallelism with the line connecting the receivers. It is to be noticed 

 that in determining the sounding angle $ this condition is approached 

 when the vessel enters shallow water. 



