Reverberation time depends on both surface absorption and time between reflections

Evidence

Clearly the length of time that it takes for sound to die is a function not only of the absorption of the surfaces in a room but also of the length of time between interactions with the surfaces of the room. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1824

Clearly the length of time it takes for sound to die is a function not only of the absorption of the surfaces in a room but also a function of the length of time between interactions with the surfaces of the room. We can use these facts to derive an equation for the reverberation time in a room. The first thing to determine is the average length of time a sound wave will travel between interactions with the surfaces of the room. This can be found from the mean free path of the room, which is a measure of the average distances between surfaces, assuming all possible angles of incidence and position. For an approximately rectangular box, the mean free path is given by the following equation: V = the volume (in m3) and S = the surface area (in m2) The time between surface interactions may be simply calculated from A4. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2815

Categorization

• DEFINE: Introduces the two physical variables — absorption and mean free path — from which the reverberation-time equation is derived.
• XREF: Ties the earlier absorption-coefficient discussion to room geometry, a key psycho-acoustic causal chain. — connects to: Reverberation time depends on room volume and surface area, not absorption alone. — Eric J. Heller, Why You Hear What You Hear- An…, 2476; Total surface area determines a material’s acoustic dominance more than its absorption coefficient alone; Ideal reverberation is a smooth exponential decay whose rate depends on context. (+12 more)
• QUESTION: Worth chasing how mean free path scales with room shape beyond the rectangular-box case.
• corroborated: 3 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1824; David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2815

Broader Connections

• Targeted absorber addition flattens reverberation time variation across frequencies #expands (0.85) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1944
• Redirecting reflections creates uneven hot spots while absorption shortens reverberation #expands (0.82)
• Total surface area can outweigh absorption efficiency in controlling room reverberation #qualifies (0.80) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1929
• Room absorption determines the steady-state level of reverberant sound #expands (0.78) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1781
• Reflected sound obeys an inverse square law in addition to surface absorption losses #expands (0.75)
• Surface reflection reduces total sound power and favors high frequencies #complicates (0.75)
• Reverberation time is defined as a 60-decibel energy decay #expands (0.72) — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 446