A room’s critical frequency depends on absorption and mode bandwidth, not just room dimensions
Evidence
What is the 60 dB reverberation time (T60) of a living room as a function of frequency whose surface area is 75 m2 and whose volume is 42 m3? The floor is carpet on concrete, the ceiling is plaster on lath, and both have an area of 16.8 m2. There are 6 m2 of windows and the rest of the surfaces are painted plaster on brick; ignore the effect of the door. Using the data in Table 6.1, set up a spreadsheet or table, as shown in Table 6.2, and calculate the equivalent open window area for each surface as a function of frequency. Having done that add up the individual surface contributions for each frequency band and apply Equation 6.20 to the result in order to calculate the reverberation time. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1929 (
#corroborates, via linked claim)
Categorization
- XREF: connects to: Axial mode frequencies are computable from room dimensions by a simple formula; Low absorption raises the real critical frequency above the mean-free-path estimate.; Larger rooms exhibit lower critical frequencies because volume scales with size — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2037 (+7 more)
Broader Connections
- Room absorption shrinks mode bandwidth and flattens standing wave peaks
#corroborates(0.90) - Physical sound absorption can be strong enough to measurably alter room reverberation
#corroborates(0.80) - Modal decay analysis governs room acoustics below the critical frequency
#expands(0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2038 - Total surface area can outweigh absorption efficiency in controlling room reverberation
#corroborates(0.75) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1929