relation for p takes the form 



p =-p B n 2 TT sinh (K.x, + \|) . )e~^ (59) 



x o - J — L - V V V 



where (47) and the identity c = J\ /p is employed. 

 Rectangular Cavity with Partially Yielding Walls 



For the more general case, the boundary condition 

 can be expressed in terms of the unit area acoustic imped- 

 ances of the walls. The boundary impedance Z is expressed 



by 



Z =B + j X =-£- (60) 



where v n is the normal component of velocity into the 

 boundary from the interior of the system. It is understood 

 that the various quantities are evaluated at the boundary 

 concerned. Using the relations for displacement and 

 pressure given by (45) and (59) it follows that at x x = 



Z x (0) = - % |^tanh 



Z^ W 

 = -tanh" 1 (61) 



On the other hand, application of (60) at the boundary 

 x z = t yields 



48 



