REGULAR COMBINATION OF ACOUSTIC ELEMENTS 



289 



where 



A = 



B = 



C 



D 



cosh Fi 



— sinh Fi 

 sinh Fi 



§|5-^sinhF2 



02 Zoi 



cosh F2 

 - sinh F2 





sinh Fa 



cosh Fr 



sinh F3 



Among these four determinants there is one relation 



AC - BD = 1, 



(57) 



(58) 



(59) 



(60) 



(61) 



as can be seen by multiplying them together. 



Hence to completely specify the characteristics of the structure 

 three parameters are required. A number of possible sets of param- 

 eters exist whose usefulness depends on the type of structure to which 

 they are applied. The set of parameters having the greatest use in 



