Enter internal room dimensions and assign a surface material to each boundary. The calculator estimates RT60—the time for sound to decay by 60 dB—at each octave band, then compares your result to published recommendations.
- Volume
- 81.0 m³
- Total surface area
- 117.0 m²
Surface Materials
Each material has a different absorption coefficient at each frequency. Harder surfaces reflect more sound (longer RT60); softer or porous surfaces absorb more (shorter RT60).
| Frequency | Absorption (sabins) | RT60 |
|---|
The recommendation compares the mid-frequency average (500 Hz & 1 kHz) against published standards. Low-frequency RT60 is typically higher and addressed separately with bass traps.
What Is RT60 Reverberation Time?
Reverberation time, denoted RT60 (or sometimes T60), is the duration required for the sound pressure level in a room to decrease by 60 decibels after a source ceases emitting. It is the single most important measurable parameter of room acoustics, and it governs whether a space sounds lively, natural, or uncomfortably echoey.
The concept was formalised by Wallace Clement Sabine at Harvard in 1898, making RT60 the oldest quantitative metric in architectural acoustics. Sabine’s original experiments—measuring the decay of organ pipe sound in Harvard’s Fogg Art Museum—directly led to the first scientifically designed concert hall: Boston Symphony Hall (1900), which remains among the most acoustically acclaimed venues in the world.
RT60 varies with frequency. Low frequencies typically decay more slowly because common building materials absorb bass poorly, while high frequencies are absorbed more readily by air itself, by carpets, and by soft furnishings. A well-designed room aims for a flat or gently sloping RT60 curve across the frequency spectrum.
The Sabine Equation Explained
Sabine’s reverberation formula relates the room’s volume to its total absorption:
RT60 = 0.161 × V / A
Here V is the volume in cubic metres, and A is the total absorption in sabins (metric), computed as the sum of each surface’s area times its absorption coefficient (α). One sabin equals one square metre of perfectly absorbing surface. The constant 0.161 has units of seconds per metre and derives from the speed of sound and the mean free path of reflections.
The Sabine equation assumes that sound energy is diffuse—evenly distributed throughout the room with reflections arriving from all directions. This holds well for rooms with moderate, evenly distributed absorption and RT60 above roughly 0.5 s. When absorption is heavy (as in a treated recording studio), the Eyring equation is more accurate:
RT60 = 0.161 × V / (−S × ln(1 − αavg))
where S is total surface area and αavg is the area-weighted mean absorption coefficient. At low absorption the two equations converge; at high absorption the Eyring equation yields shorter (more realistic) RT60 values.
RT60 Values for Different Room Types
The optimal reverberation time depends entirely on the room’s intended use. Speech intelligibility demands short RT60 so that each syllable decays before the next arrives. Music, particularly orchestral or choral repertoire, benefits from a longer sustain that blends notes and adds richness. The following values represent established design targets:
| Room type | Ideal RT60 (mid-frequency) | Rationale |
|---|---|---|
| Recording studio | 0.2–0.4 s | Minimise room sound; capture only the source |
| Control room | 0.25–0.4 s | Accurate monitoring requires neutral acoustics |
| Classroom / lecture hall | 0.4–0.6 s | Speech clarity for the full audience |
| Open-plan office | 0.5–0.8 s | Reduce noise propagation between workstations |
| Living room | 0.4–0.7 s | Natural conversation comfort |
| Concert hall | 1.5–2.5 s | Blend and sustain musical notes for richness |
How to Reduce Reverberation Time
Reducing RT60 means increasing total absorption. The practical approaches, in order of effectiveness:
- Porous absorbers (mineral wool, fibreglass, open-cell foam): most effective above 500 Hz. Thicker panels absorb lower; 10 cm panels extend useful absorption to roughly 250 Hz. Mount panels with an air gap behind them to increase low-frequency performance without additional thickness.
- Membrane absorbers (sealed panel traps): a mass (plywood, MDF) over a sealed air cavity resonates at a specific frequency, absorbing a narrow low-frequency band. Useful for targeting a problematic mode or bringing the 125 Hz RT60 in line with higher frequencies.
- Carpet and soft furnishings: effective at high frequencies but contribute almost nothing below 250 Hz. Relying solely on carpet produces an unbalanced RT60 curve—dead highs with boomy lows.
- Diffusion does not change RT60 but redistributes reflections in time and direction, improving perceived evenness. Combine with absorption for the best perceptual result.