The field of building acoustics consists of two parts; Room Acoustics which deals with sound propagation in a room and Building Acoustics, which deals with sound propagation between rooms.
Typically, room acoustics is related to the quality of sound, e.g. concert hall acoustics, while building acoustics is more related to unwanted sound, i.e. when you want to hear as little as possible of what is going on in adjacent rooms. From a measurement technology point of view, the two have a lot in common which shall be outlined here.
Sound in a Room
Assume that we put our sound level meter in a fixed position in a room and that we start a sound source. The sound source could be amachine or a combination of a noise generator, a power amplifier and a loudspeaker or anything else making enough noise to make useful measurements.
What we will observe now is that the sound pressure level in the room will not rise indefinitely as the sound source continues to “pour” noise energy into the room. Instead, the sound level stabilises.
Why is that?
Simply because the rate of sound energy input to the room is exactly compensated by the rate of energy absorbed in the room.