An open window is the acoustic reference standard with absorption coefficient 1

Evidence

If a steady tone, such as an organ note, is played in the space then after a period of time the reverberant sound will reach a constant level because at that point the sound power input balances the power lost by absorption in the space. This means that the steady-state level will be higher in rooms that have a small amount of absorption, compared with rooms that have a lot of absorption. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1781 (#qualifies, via linked claim)

Categorization

• XREF: connects to: Room absorption determines the steady-state level of reverberant sound — David Howard, Jamie Angus, coustics and Psychoacoustics, 1781; Air absorption can be modeled as equivalent surface absorption scaled by room volume

Broader Connections

• Room absorption determines the steady-state level of reverberant sound #qualifies (0.75) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1781
• Air absorption can be modeled as equivalent surface absorption scaled by room volume #expands (0.75)