How the Eyring reverberation time calculator works
Enter room length, width, height, and an average absorption coefficient α. The tool computes room volume and total surface area, then estimates T60 with both the Sabine formula (T = 0.161 × V / A) and the Eyring formula (T = −0.163 × V / (S × ln(1 − α))) so you can compare results side by side. The difference between the two predictions reveals how much a room's treatment level matters for accuracy.
Why Eyring is more accurate in treated rooms
Sabine's formula was derived under the assumption that sound energy is distributed uniformly and each reflection has an equal probability of being absorbed. This holds reasonably well in lightly damped rooms where sound bounces many times before dying out. In a heavily treated space, however, much of the energy is absorbed in the first few reflections. Sabine does not account for this early absorption and therefore overestimates the reverberation time. The Eyring formula uses a logarithmic term that correctly handles high-absorption scenarios, giving a shorter and more accurate T60 prediction as α increases above 0.2.
How to estimate the average absorption coefficient
The average absorption coefficient α is a single number that represents all room surfaces combined. To calculate it precisely, multiply each surface area by its published absorption coefficient at the frequency of interest, sum all those values, and divide by the total surface area of the room. In practice, for initial planning you can estimate: α ≈ 0.05–0.10 for untreated concrete or plaster; α ≈ 0.15–0.25 for a furnished living room; α ≈ 0.30–0.50 for a lightly treated studio; α ≈ 0.50–0.70 for a heavily treated recording room. You can also back-calculate α from a measured T60 by rearranging either formula.
When the two formulas agree and when they diverge
At very low absorption values (α below 0.1), Sabine and Eyring produce nearly identical results because ln(1 − α) ≈ −α for small α. The divergence grows with absorption: at α = 0.3, Eyring predicts a T60 roughly 15% shorter than Sabine; at α = 0.5, the difference exceeds 40%. This matters practically when you are designing a voice-over booth or a heavily deadened listening room — using Sabine would lead you to under-treat the space.
Key terms
- T60 — time for sound level to drop 60 dB after the source stops; describes how live or dead a room sounds to a listener.
- Sabine formula — T = 0.161 × V / A; works well for rooms with average α below 0.2.
- Eyring formula — T = −0.163 × V / (S × ln(1 − α)); more accurate in treated rooms where α exceeds 0.2.
- α (alpha) — average absorption coefficient for all room surfaces; ranges from 0 (perfectly reflective) to values approaching 1 (fully absorbing).
- Total surface area S — sum of floor, ceiling, and all wall areas; used in the Eyring denominator together with α.
Frequently asked questions
- When should I use Eyring instead of Sabine? Use Eyring when the average absorption coefficient exceeds about 0.2 — for example, in treated recording studios, broadcast rooms, or offices with heavy soft furnishings. Sabine overestimates T60 in these cases because it assumes sound bounces many times before being absorbed, which does not happen in a heavily damped room.
- What is T60? T60 is the time, in seconds, for sound pressure level to decay by 60 dB after the source stops. It describes how live or reverberant a room feels. A short T60 (under 0.3 s) sounds dry and dead; a long T60 (above 1 s) sounds live and reverberant.
- What absorption coefficient should I enter? Enter the average absorption coefficient for all room surfaces combined. Untreated concrete or plaster rooms average around 0.05–0.10. A typical furnished living room sits around 0.15–0.25. A treated recording studio may reach 0.35–0.60 or higher. You can estimate by weighting each surface's published alpha value by its area.
- Why does the Eyring formula give a lower T60 than Sabine? Eyring uses −ln(1 − α) in the denominator, which grows faster than the simple α used by Sabine. This means for the same absorption coefficient, Eyring predicts a shorter decay time. The difference is negligible below α = 0.1 but becomes substantial above α = 0.3.
- What T60 should a home studio aim for? A small home studio mixing room typically targets 0.25–0.40 s average, with as little variation as possible across octave bands. A T60 that is much longer at low frequencies than at mid-range indicates insufficient bass trapping and will cause unreliable low-end mix decisions.
- How do I measure alpha for my room? You can back-calculate alpha from a measured T60 using the Sabine or Eyring formula rearranged for α. Measure T60 using Room EQ Wizard (REW) and a measurement microphone, then solve for α. This gives you a real-world starting point for treatment planning calculations.