An audience’s breathing and perspiration dynamically alter a hall’s high-frequency acoustics

Evidence

Equations 6.17 and 6.18 show that the reverberation time depends on the volume, surface area, and the average absorption coefficient in the room. However, the absorption coefficients of real materials are not constant with frequency. This means that, assuming that the room’s volume and surface area are constant with frequency, which is not an unreasonable assumption, the reverberation time in the room will also vary with frequency. This will subjectively alter the timbre of the sound in the room due to both the effect on the level of the reverberant field discussed earlier and the change in timbre as the sound in the room decays away. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1876 (#expands, via linked claim)

Equation 6.16 gives us the time between surface interactions, and at each of these interactions, α is the proportion of the energy absorbed, where α is the average absorption coefficient discussed earlier. If α of the energy absorbed at the surface, then (1 − α) is the proportion of the energy reflected back to interact with further surfaces. At each surface a further proportion, α, of energy will be removed, so the proportion of the original sound energy that is reflected will reduce exponentially. The combination of the time between reflections and the exponential decay of the sound energy, through progressive interactions with the surfaces of the room, can be used to derive an expression for the length of time that it would take for the initial energy to decay by a given ratio. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1830 (#expands, via linked claim)

Categorization

• XREF: connects to: Occupied audiences absorb up to 90 percent of incident sound in a hall; Room sound energy decays exponentially through repeated surface absorptions — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1830; Room reverberation time varies with frequency, altering perceived timbre — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1876 (+1 more)

Broader Connections

• Room reverberation time varies with frequency, altering perceived timbre #expands (0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1876
• Room sound energy decays exponentially through repeated surface absorptions #expands (0.72) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1830
• Physical sound absorption can be strong enough to measurably alter room reverberation #expands (0.72)