and hence 



/ = 5204 c/s 



This value is in good agreement with the experimental 

 results for cavity No. 2. 



An estimate of the acoustic loss suffered by radiation 

 into the surrounding air can be determined by assuming 

 that the air load is 42 acoustic ohms (i. e. , r - r 2 = r 3 = 84 

 acoustic ohms). The generalized counterpart of (70) is 



17 n i 

 p oj I. 2 rt 



Combining this with relations (65) yields 



I 



TT p > h * 



The latter quantity gives the temporal attenuation rate in 



neper/ sec. The corresponding spatial attenuation factor 



a = a, /c. Using the above relations with the assumed 



o t 



value of r and the previous values of h. gives a = 1. 66 



neper/kyd, which corresponds to 19.2 db/kyd. 



This is of the same order of magnitude as the losses 

 determined experimentally for the cavity filled with pure 

 water. The viscous attenuation due to the pure water, for 

 the same size cavity, is only of the order of 0. 5 db/kyd as 

 estimated from the relations in the following section. 



Cavity with Internal Losses plus Radiation 



The theory of a resonant cavity developed in the pre- 

 ceding is only applicable when the fluid is essentially 



(73) 



54 



