Spoken Word Reverberation Time Estimator
Estimates the RT60 reverberation time — the time for sound to decay by 60 dB — for a room, optimised for spoken word intelligibility. Uses both the Sabine and Eyring formulas.
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Formulas
Sabine Formula:
RT60 = 0.161 × V / A
where V = room volume (m³), A = total absorption = S·α + Aextra (m² Sabins)
Eyring Formula (more accurate for α > 0.2):
RT60 = 0.161 × V / (−S × ln(1 − αeff))
where αeff = A / S (effective mean absorption coefficient)
Surface Area:
S = 2(LW + LH + WH)
The constant 0.161 = 24 × ln(10) / c, where c ≈ 343 m/s (speed of sound at 20°C).
Assumptions & References
- Room is assumed to be a rectangular shoebox with uniform surface absorption.
- Absorption coefficient α is a single broadband value (mid-frequency, ~1 kHz is most representative for speech).
- Additional absorption (furniture, audience, fittings) is entered separately in metric Sabins (m²).
- Speed of sound assumed at 343 m/s (20°C, dry air).
- Sabine formula is most accurate for low absorption (α < 0.2); Eyring is preferred for higher absorption.
- Optimal RT60 for speech intelligibility: 0.4 – 0.8 s per ISO 3382-2 and IEC 60268-16 (STI standards).
- References: Sabine, W.C. (1900); Eyring, C.F. (1930); ISO 3382-2:2008; Kuttruff, H. — Room Acoustics (5th ed.).