Reverberation Time Calculator
Free Reverberation time Calculator for acoustic waves. Enter variables to compute results with formulas and detailed steps.
Formula
RT60 = 0.161 V / A (Sabine) or RT60 = 0.161 V / (-S ln(1-alpha)) (Eyring)
Where RT60 is reverberation time in seconds, V is room volume in cubic meters, A is total absorption in sabins (sum of surface area times absorption coefficient), S is total surface area, and alpha is the average absorption coefficient. The factor 0.161 has units of seconds per meter.
Worked Examples
Example 1: Classroom Reverberation Assessment
Problem: A classroom is 10m x 8m x 3m with average absorption coefficient of 0.15. Calculate RT60 using both Sabine and Eyring equations.
Solution: Volume = 10 x 8 x 3 = 240 m3\nTotal surface area = 2(10x8) + 2(10x3) + 2(8x3) = 160 + 60 + 48 = 268 m2\nTotal absorption A = 268 x 0.15 = 40.2 sabins\nSabine RT60 = 0.161 x 240 / 40.2 = 38.64 / 40.2 = 0.961 s\nEyring RT60 = 0.161 x 240 / (-268 x ln(0.85)) = 38.64 / (-268 x -0.1625) = 38.64 / 43.56 = 0.887 s
Result: Sabine RT60: 0.961 s | Eyring RT60: 0.887 s (classroom target is 0.4-0.7 s, treatment needed)
Example 2: Concert Hall Design Target
Problem: A concert hall has volume 12,000 m3. What total absorption is needed for RT60 = 2.0 seconds?
Solution: Using Sabine: RT60 = 0.161 x V / A\nRearranging: A = 0.161 x V / RT60\nA = 0.161 x 12000 / 2.0 = 1932 / 2.0 = 966 sabins\nIf total surface area is approximately 4000 m2\nRequired average alpha = 966 / 4000 = 0.24\nCritical distance = 0.057 x sqrt(12000/2.0) = 0.057 x 77.5 = 4.4 m
Result: Total Absorption Needed: 966 sabins | Average alpha: 0.24 | Critical Distance: 4.4 m
Frequently Asked Questions
What is reverberation time (RT60) and why is it important in room acoustics?
Reverberation time RT60 is the time in seconds for sound to decay by 60 decibels after the source stops. It is the single most important parameter in room acoustics because it determines how sounds blend, overlap, and sustain in a space. A room with too long an RT60 causes speech to become unintelligible as syllables overlap each other. A room with too short an RT60 sounds dead and uncomfortable, lacking warmth and natural ambiance. Concert halls typically target 1.8-2.2 seconds for orchestral music, while classrooms need 0.4-0.7 seconds for clear speech. Recording studios often aim for very controlled, short reverberation times around 0.3-0.5 seconds.
How does air absorption affect reverberation in large spaces?
Air absorbs sound energy during propagation, with the absorption increasing with frequency, temperature, and humidity. At room temperature and moderate humidity, air absorption is negligible below 1 kHz but becomes significant above 2 kHz, especially in large spaces where sound travels long distances between reflections. In a cathedral or large arena with mean free paths of 10-20 meters, air absorption can reduce the high-frequency RT60 by 30-50 percent compared to wall absorption alone. This is why large reverberant spaces often sound warm and muffled, with strong low-frequency reverberation but rapidly decaying high frequencies. The Sabine equation accounts for this with an additional 4mV term, where m is the air attenuation coefficient in inverse meters.
What are room modes and how do they relate to reverberation at low frequencies?
Room modes are standing wave resonances that occur at frequencies where the room dimensions equal integer multiples of half wavelengths. There are three types: axial modes (between two parallel surfaces), tangential modes (involving four surfaces), and oblique modes (involving all six surfaces). Below the Schroeder frequency, the room response is dominated by individual modes creating uneven frequency response with peaks and nulls. Above the Schroeder frequency, modes overlap sufficiently to create a statistically diffuse sound field where the Sabine and Eyring equations are valid. The Schroeder frequency equals approximately 2000 times the square root of RT60/V. For a small room (50m3, RT60=0.5s), this is about 200 Hz, meaning modal behavior dominates the entire bass range.
How can reverberation time be measured in an existing room?
RT60 is measured by exciting the room with a broadband sound source and recording the decay after the source stops. The traditional method uses an impulsive source (balloon pop, starter pistol) or interrupted noise, with measurement microphones and analysis software calculating the decay rate from the impulse response. Modern methods use swept-sine signals or maximum-length sequences that provide better signal-to-noise ratio. Measurements should be taken at multiple source and receiver positions to account for spatial variation, especially below the Schroeder frequency. Standards like ISO 3382 specify procedures for measurement positions, source types, and analysis methods. Low-cost measurement systems using smartphones with calibrated microphones can achieve acceptable accuracy for basic assessments.
What practical steps can reduce excessive reverberation in a room?
To reduce RT60, add sound-absorbing materials to room surfaces. The most effective approach targets the largest untreated surfaces first. Adding acoustic ceiling tiles (alpha 0.5-0.9) to a hard ceiling dramatically reduces RT60 because the ceiling is typically the largest unobstructed surface. Wall-mounted absorptive panels covering 30-50 percent of wall area provide significant improvement. Carpet reduces high-frequency RT60 but has minimal effect at low frequencies. Heavy curtains spaced from walls absorb effectively at mid to high frequencies. For bass control, thick porous absorbers (minimum 10 cm) or membrane absorbers tuned to problematic frequencies are needed. Upholstered furniture and audience members also contribute absorption, which is why empty concert halls sound more reverberant than occupied ones.
Can I use Reverberation Time Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.