Room Acoustics: RT60 and Axial Modes
Reverberation time (RT60) and the first axial room modes that cause bass buildup.
Example
You enter
- Room volume (ft³) 5000
- Total absorption (sabins) 500
- Room length (ft) 20
- Room width (ft) 15
- Room height (ft) 10
You get
- Reverberation time (RT60) 0.49 s
- First axial mode (length) 28.3 Hz
- First axial mode (width) 37.7 Hz
- First axial mode (height) 56.5 Hz
Checked against published worked examples from: University of Illinois (S. Errede), after Backus, The Acoustical Foundations of Music.
Details, formula, and sources
ScopeReverberation time from the Sabine equation (0.049 x volume / total sabins) plus the three first axial room modes c/(2 x dimension) that predict bass buildup and nulls. The room half of the live-production acoustics math, alongside the inverse-square and atmospheric-absorption SPL calculators.
Formula or tableRT60 = 0.049 x V / A (Sabine, imperial); first axial mode per dimension = c / (2 x length), c = 1130 ft/s.
Source and editionW.C. Sabine reverberation equation (public domain); axial room-mode relation f = c / (2 x L) from first-principles standing-wave acoustics.
Free accessSabine's collected papers and the half-wavelength room-mode relation are public-domain physics.
What governsEstimate. AHJ and licensed professional govern.
API field namesvolume_ft3, total_sabins, length_ft, width_ft, height_ft, rt60_s, mode_L_hz, mode_W_hz, mode_H_hz
- Sabine coefficient 0.049 (imperial, ft and ft^3; default, editable)Sabine equation
- Speed of sound 1130 ft/s at room temperature (default, editable)First-principles acoustics