the form 



Yy+N 2 



where y is a transmission coefficient which gives the frac- 

 tion of incident energy flux which leaks through the boundary. 

 The ratio V/A defines a characteristic dimension L for the 

 cavity (V being the volume and A the surface area). Thus 

 the above relation can be written 



f +eoo s 



Bearing in mind that this should correspond to 2 ct£, where 

 ci£ is the amplitude decay modulus, it is seen that this is 

 consistent with (76b) provided that 



Y=2i-Va-/f, (77) 



The quantity on the right can be shown to be directly pro- 

 portional to the impedance ratio r/p c as should be expected 

 provided that the ratio is suitably small. The factor of 

 proportionality depends upon the shape of the cavity and the 

 particular mode of oscillation. 



Practical Relations Implied by the Theory 



The result (76b) for the temporal decay factor pertinent 

 to a resonant cavity consists of two parts 



fa *> total =«H' + <«*> ex <™> 



where (a^) is the attenuation factor associated with the 

 particular properties of the cavity and (a^) represents 

 excess attenuation associated with the contained fluid. 



57 



