(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 =