(a) Sound transmission coefficient
(T):
It is the ratio which the sound energy
of a given frequency transmitted through a surface to that incident on it.
(b) Sound Reduction Index (SRI):
(11)
For composite partitions of n nos. of
surface parts, the average transmission coefficient TAV
can be found from the following equation:
(12)
where Ti
= transmission coefficients of the ith part
Ai =
area of the ith part
A = total area of partition = 
