1.07
s
1.01
s
250
m²
0.12
1.07
s
1.01
s
250
m²
0.12
The Reverberation Time Calculator estimates how long sound persists in an enclosed space after the source stops. Reverberation time (RT60) is the most important single parameter in room acoustics, determining whether a space sounds lively, clear, or muddy. This tool calculates RT60 using both the Sabine equation and the more accurate Norris-Eyring formula, helping architects, acoustic engineers, and audio professionals design spaces with appropriate acoustic characteristics.
Reverberation time RT60 is defined as the time for sound to decay by 60 dB (a factor of one million in intensity) after the source stops. The classic Sabine equation is:
$$RT_{60} = \frac{0.161 \cdot V}{A}$$
where $$V$$ is the room volume in m³, $$A$$ is the total absorption in metric sabins (m²), and 0.161 is derived from the speed of sound ($$24 \ln(10)/c \approx 0.161$$ at 343 m/s).
The total absorption $$A$$ is the sum of each surface's area multiplied by its absorption coefficient: $$A = \sum S_i \cdot \alpha_i$$.
For rooms with higher absorption (average $$\bar{\alpha} > 0.2$$), the Norris-Eyring equation is more accurate:
$$RT_{60} = \frac{0.161 \cdot V}{-S \cdot \ln(1 - \bar{\alpha})}$$
where $$S$$ is the total surface area and $$\bar{\alpha} = A/S$$ is the average absorption coefficient. The Sabine equation overestimates RT60 in highly absorptive rooms because it does not account for the diminishing returns of absorption.
Optimal RT60 depends on the room's purpose: speech clarity requires shorter times (0.4–0.8 s for classrooms, 0.6–1.2 s for lecture halls), while music benefits from longer reverberation (1.4–2.0 s for concert halls, 2.0–4.0 s for cathedrals). A recording studio control room typically aims for 0.3–0.4 s. If your calculated RT60 is too long, increase absorption (add acoustic panels, carpeting, or soft furnishings). If too short, reduce absorption (use reflective surfaces).
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Results
Sabine RT60 = 0.161 × 200/30 = 1.07 s. For speech, this is slightly long — adding acoustic panels to bring A up to ~45 m² sabins would reduce RT60 to ~0.72 s, ideal for a classroom.
Inputs
Results
With very high absorption this gives a short RT60. Concert halls typically need much less absorption. A realistic A ≈ 4000 sabins for 15,000 m³ gives RT60 ≈ 0.6 s — very dry for a concert hall, which ideally has RT60 of 1.5–2.0 s.
A sabin (or metric sabin, m²) is the unit of sound absorption. One metric sabin equals the absorption provided by 1 m² of a perfectly absorbing surface (α = 1.0). A 10 m² wall with an absorption coefficient of 0.3 provides 3 metric sabins of absorption.
Use Norris-Eyring when the average absorption coefficient exceeds about 0.2. The Sabine equation assumes low absorption and overestimates RT60 in well-treated rooms. For highly absorptive spaces (recording studios, anechoic chambers), Norris-Eyring gives significantly more accurate predictions.
For speech, RT60 should be 0.4–0.8 seconds in small rooms (classrooms, meeting rooms) and 0.6–1.2 seconds in larger spaces (lecture halls, theaters). Longer reverberation causes words to overlap and reduces intelligibility. The Speech Transmission Index (STI) is the professional metric for speech clarity.
It depends on the genre: chamber music works well at 1.2–1.5 s, symphonic music at 1.6–2.2 s, romantic orchestral at 1.8–2.5 s, and organ music or choral in 2.5–4.0+ s in cathedrals. Rock and pop studios typically aim for 0.3–0.5 s (dry) with artificial reverb added in mixing.
Significantly. Upholstered furniture, carpets, curtains, and even people absorb sound. A room full of people can have 20–40% more absorption than an empty room. This is why spaces are designed to meet RT60 targets at expected occupancy levels.
The absorption coefficient (α) ranges from 0 (perfectly reflective, like marble) to 1 (perfectly absorptive, like an open window). Typical values: concrete 0.02, glass 0.04, carpet on concrete 0.3, acoustic foam 0.6–0.9, heavy curtains 0.5–0.75. Values vary with frequency.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
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