In simple nonmathematical terms, the impulse response is the sound level versus time curve when the room has been excited by an impulse sound (e.g., a clap). Nowadays, it can be processed from measurements and computer simulations using dedicated software.
The impulse response can bring useful indications regarding the behavior of a room that goes far beyond the mere reverberation time value. It will indicate the various contributions from reflections, and using the time interval between initial signal emission and reflection arrival, it will then be possible to determine the path followed by that particular contribution. While the impulse response as a measurement result will sometimes need some head scratching to find out which path has been followed, as a computer simulation result it usually is possible to follow precisely such a path and take appropriate measures if need be.
Figure 6.1 shows an example from a badly treated Italian-style opera hall. Looking at the stylized impulse response, it can be seen that after the direct sound has reached the measurement point, there are a few reflections, and then there is a massive arrival of reflected sound; this comes from the fact that such a facility features a curved cupola, curved balconies, and
Figure 6.1 Example of stylized impulse response curve.
a curved proscenium, whose reflections arrive near simultaneously more than 40 ms after the direct sound.