The Sabine equation works well when absorption coefficients stay under 0.3

Evidence

Equation A5.3 is also known as the “Millington–Sette equation.” Although Equation A5.3 can be used irrespective of the absorption level it is still more complicated than the Sabine equation, and if the absorption coeffi­ cient is less than 0.3 it can be approximated very effectively by it, as dis­ cussed previously. Thus in many contexts the Sabine equation, Equation A5.1, is preferred. — David Howard, Jamie Angus, coustics and Psychoacoustics, 2848

Equation 6.21 is also known as the “Millington–Sette equation.” Although Equation 6.21 can be used irrespective of the absorption level it is still more complicated than the Sabine equation and, if the average absorption coefficient is less than 0.3, it can be approximated very effectively by it, as discussed previously. Thus in many contexts the Sabine equation, Equation 6.20, is preferred. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1931

Categorization

• DEFINE: Establishes the practical rule of thumb: below absorption 0.3, the simpler Sabine equation suffices.
• corroborated: 3 independent passages support this claim — David Howard, Jamie Angus, coustics and Psychoacoustics, 2848; David Howard, Jamie Angus, coustics and Psychoacoustics, 1931
• XREF: connects to: The Sabine formula assumes diffuse sound that real rectangular rooms rarely produce; Rectangular rooms fail to randomize sound directions, violating Sabine theory; Room materials’ absorption coefficient varies with frequency (+3 more)

Broader Connections

• Sabine’s reverberation formula founded architectural acoustics but fails for high absorption #expands (0.85)
• Modal absorption is frequency dependent, stretching decay time at standing-wave frequencies #qualifies (0.80)
• Room materials’ absorption coefficient varies with frequency #qualifies (0.78)
• A 20x24x9 ft room needs 530 sabins of absorption for 0.4 s RT #exemplifies (0.70)