Unevenly absorbed or coupled spaces produce multi-sloped decay curves instead of one smooth exponential.

Evidence

Figure 6.14, on the other hand, shows two situations in which the reverberant field is no longer diffuse. In the first situation all the absorption is only on two surfaces, for example an office with acoustic tiles on the ceiling, carpets on the floor, and nothing on the walls. Here the sound between the absorbing surfaces decays quickly, whereas the sound between the walls decays much more slowly due to the lower absorption. In the second case, there are two connected spaces, such as the transept and nave in a church or under the balconies in a concert hall. In this case, the sound energy does not couple entirely between the two spaces, and so they will decay at different rates that depend on the level of absorption in them. In both of these cases, the result is a sound energy curve as a function of time that has two or more slopes, as shown in Figure 6.15. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1865

Categorization

• QUESTION: How much of what we hear as a space’s ‘character’ is really these two-slope decays?
• SEED: Angle: the acoustics of office carpet-and-tile monotony versus the layered decay of a church nave.