Purpose and frequency bands#
Room Analysis estimates reverberation time in six octave bands: 125, 250, 500, 1,000, 2,000 and 4,000 Hz. It supports individual-room refinement and project-wide review against selected acoustic targets.
Room quantities and assignments#
Analysis volume is derived from floor area multiplied by analysis height. Review the effective quantities and applicable overrides, especially with variable ceiling heights, sloping roofs or complex spaces.
Analysis height is derived from available Revit room and model information. Where the primary geometry is unavailable or unsuitable, Acouso may use alternative model-derived quantities. Review the effective height for complex or irregular spaces.
Assigned constructions establish the baseline acoustic materials. Room-specific finishes and treatments change the exposed acoustic composition. The equations use exposed assigned areas rather than every material layer in the construction.
Equivalent absorption area
Equivalent absorption area combines the exposed area and effective absorption of each assigned surface in an octave band.
- A
- Equivalent absorption area (m²)
- Sᵢ
- Exposed area of surface or assigned patch i (m²)
- αᵢ
- Effective band absorption coefficient for that patch (dimensionless)
C. F. Eyring (1930), Reverberation Time in “Dead” Rooms.
Area-weighted mean absorption
This area-weighted coefficient summarises the room’s assigned absorption in an octave band.
- ᾱ
- Area-weighted mean coefficient (dimensionless)
- A
- Equivalent absorption area (m²)
- S, Sᵢ
- Total area and individual exposed areas (m²)
C. F. Eyring (1930), Reverberation Time in “Dead” Rooms.
Reverberation methods#
The available methods are Sabine, Norris–Eyring and Millington–Sette. The Acouso option selects among them according to the room's absorption characteristics; results identify the selected formula. Automatic selection still relies on the assumptions of these statistical methods.
Reverberation constant
Room Analysis uses a sound speed of 343 m/s, giving a reverberation constant of approximately 0.161 s/m.
- k
- Reverberation constant (s/m)
- c
- Sound speed; Room Analysis uses 343 (m/s)
C. F. Eyring (1930), Reverberation Time in “Dead” Rooms.
Sabine reverberation time
Sabine estimates reverberation time from room volume and equivalent absorption area under diffuse-field assumptions.
- T₆₀
- Estimated time for a 60 dB decay (s)
- k
- Reverberation constant (s/m)
- V
- Effective analysis volume (m³)
- A
- Equivalent absorption area (m²)
C. F. Eyring (1930), Reverberation Time in “Dead” Rooms.
Norris–Eyring reverberation time
Norris–Eyring estimates reverberation time from room volume, exposed surface area and effective mean absorption.
- T₆₀
- Estimated time for a 60 dB decay (s)
- k
- Reverberation constant (s/m)
- V
- Effective analysis volume (m³)
- S
- Total exposed surface area (m²)
- ᾱ
- Effective area-weighted mean coefficient, limited below one for this logarithm (dimensionless)
C. F. Eyring (1930), Reverberation Time in “Dead” Rooms.
Millington–Sette reverberation time
Millington–Sette accounts for each surface’s exposed area and effective absorption when estimating reverberation time.
- T₆₀
- Estimated time for a 60 dB decay (s)
- k
- Reverberation constant (s/m)
- V
- Effective analysis volume (m³)
- Sᵢ
- Exposed area of patch i (m²)
- αᵢ
- Effective patch coefficient, limited below one for this logarithm (dimensionless)
Room Analysis uses a sound speed of 343 m/s and contains no separate atmospheric-loss term. Atmospheric attenuation in the ray workflow has its own calculation basis.
Worked Sabine example#
| Input | Example value |
|---|---|
| Floor area × analysis height | 80 m² × 2.5 m |
| Analysis volume V | 200 m³ |
| Total exposed area S | 250 m² |
| Uniform effective absorption coefficient | 0.16 in the selected band |
| Equivalent absorption area A | 250 × 0.16 = 40 m² |
With k approximately 0.161 s/m, Sabine gives T60 approximately 0.161 × 200 / 40 = 0.81 s. This is one illustrative octave-band calculation, not a benchmark or a prediction for a particular real room.
Treatment estimates and target comparisons#
A treatment-area estimate is a method-dependent design aid. It depends on the selected formula, existing absorption, treatment properties and target. Review the actual area distribution and recalculate after changing materials; an equivalent-absorption deficit is not automatically an installable treatment area.
Target comparisons use the selected project criteria and reporting bands. A summary result can combine selected bands, so inspect the band values as well as the summary.
Assumptions and limitations#
These methods assume a diffuse sound field. They do not predict position-dependent reflections or low-frequency room modes. Unusual geometry, uneven absorption and coupled spaces require particular care. Meeting the chosen target in the model does not certify the installed room.