In estimating the Insertion Loss of a barrier installed in a large room the following
assumptions are implicit:
(1) The transmission loss of the barrier material is sufficiently large that transmission through
the barrier can be ignored. A transmission loss of 20 dB is recommended.
(2) The sound power radiated by the source is not affected by insertion of the barrier.
(3) The receiver is in the shadow zone of the barrier; that is, there is no direct line of sight
between source and receiver.
(4) Interference effects between waves diffracted around the side of the barrier, waves diffracted
over the top of the barrier and reflected waves are negligible. This implies octave band
analysis.
Barriers are ineffective in a highly reverberant environment. The performance of an indoor
barrier is always improved by hanging absorptive baffles from the ceiling or by placing sound
absorbing material directly on the ceiling (see Figure 10.24).