Low absorption raises the real critical frequency above the mean-free-path estimate.
Evidence
This expression is useful for making a rapid assessment of the likelihood of achieving a particular critical frequency in a given room. However, the real critical frequency may well be higher because a room can have significant modal behavior at high frequencies if the absorption is low. Because of this the accepted definition of critical frequency is based on the mode bandwidth, although this can result in a chicken and egg situation at the initial design stages, hence the earlier equation. — David Howard, Jamie Angus, coustics and Psychoacoustics, 2083
Categorization
Category: Causal Relationships
- QUESTION: The chicken-and-egg problem at initial design stages is worth understanding better: how do designers break in with values they don’t yet know?
Related
- Modal bandwidths break diffuse-field assumptions when sound paths exceed the mean free path (similarity 0.80)
- Resistive absorbers only work where air particles move, which pushes them to high frequencies (similarity 0.79)
- Modal behavior intensifies as wavelength approaches the room’s mean free path (similarity 0.79)
- Room materials’ absorption coefficient varies with frequency (similarity 0.78)
Broader Connections
- A room’s critical frequency depends on absorption and mode bandwidth, not just room dimensions
#expands(0.78) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2033 - Higher frequencies produce higher particle velocities, improving porous absorber efficiency
#contradicts(0.70) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2045