Answers to the most common questions about RT60 reverberation time, the Sabine and Eyring formulas, absorption coefficients, room acoustic targets, and the tools on Reverb-Calculator.com.
About the Tools
What does the Reverb Calculator do?
The Reverb Calculator takes three inputs — room volume, total surface area, and average absorption coefficient — and returns the RT60 reverberation time in seconds using the Sabine formula (RT60 = 0.161 × V/A in metric units). It is a pure mathematical calculation tool. No microphone, no audio capture, and no browser permissions are required beyond basic JavaScript. Full technical documentation is in the How It Works page.
Does the calculator require microphone access or any audio?
No. Despite being an “acoustics” tool, the Reverb Calculator works entirely from typed numeric inputs — room dimensions and absorption coefficient values. It performs arithmetic on those numbers and returns a result. No sound is captured, no microphone is accessed, and no Web Audio API is used. Full details are in the Data Security page.
What is the difference between the Sabine and Eyring calculators?
Both calculate RT60, but they use different formulas that give different accuracy depending on how absorptive the room is.
Sabine formula: RT60 = 0.161 × V/A — simpler, works well for rooms with low average absorption (coefficient below approximately 0.15–0.20). Most untreated or lightly treated rooms.
Eyring formula: RT60 = 0.161 × V / (−S × ln(1−ᾱ)) — more accurate for rooms with higher absorption (average coefficient above 0.30), such as recording studios, vocal booths, and heavily treated home theatres. At high absorption values, the Sabine formula overestimates RT60 significantly.
If you are calculating RT60 for a well-treated studio or a heavily furnished room, use the Eyring calculator. For untreated or lightly treated rooms, either formula gives similar results.
RT60 Fundamentals
What is RT60?
RT60 is the time it takes for sound pressure level to decay by 60 decibels in an enclosed space after the sound source stops. It is the standard measurement of reverberation in architectural acoustics. A higher RT60 means a more reverberant room; a lower RT60 means a drier, less reflective room. The “60” refers to the 60 dB decay standard established by Wallace Clement Sabine at Harvard University in 1898.
What is a good RT60 for a recording studio?
Recording studios typically target RT60 between 0.3 and 0.6 seconds. Control rooms and mixing rooms, where accurate monitoring is critical, usually target a shorter RT60 of 0.2 to 0.4 seconds. Vocal booths need the shortest RT60 — typically 0.2 to 0.4 seconds — to capture dry, clean vocals without room reflections colouring the recording. These ranges reflect the need for controlled, minimally reverberant acoustic environments where the recording captures the source rather than the room.
What is a good RT60 for a classroom?
Classrooms for general teaching are typically designed for RT60 between 0.6 and 0.9 seconds. This range supports speech intelligibility — enough absorption to prevent excessive echo and reverb tail that masks speech, but not so much that the room feels uncomfortably dead. For hearing-impaired students or large lecture theatres, shorter RT60 values (0.4–0.7 seconds) are preferred. WHO and ISO guidelines for classroom acoustics address both RT60 and background noise levels as joint determinants of speech intelligibility.
What is a good RT60 for a concert hall?
Concert halls for orchestral music are typically designed with RT60 between 1.5 and 2.5 seconds at mid-frequencies. This longer reverberation time gives the music its richness, warmth, and spatial envelopment — qualities that listeners associate with fine acoustic concert spaces. Chamber music halls, where smaller ensembles perform, typically use shorter RT60 of 1.3 to 1.8 seconds. Opera houses typically target 1.2 to 1.6 seconds — shorter than symphony halls because text intelligibility matters alongside musical richness.
Why does RT60 matter for home theatres?
Home theatres need a controlled acoustic environment that serves both dialogue intelligibility and cinematic music and effects. Most acoustic designers target RT60 between 0.3 and 0.5 seconds for home theatres — shorter than a living room but not as dry as a recording studio. Too much reverberation smears dialogue and blurs low-frequency bass impact. Too little reverberation can feel unnaturally clinical for music and ambience content.
The Formulas
What does the Sabine constant 0.161 mean and where does it come from?
The Sabine constant is derived from the physics of sound propagation in air. The formula for RT60 comes from modelling sound energy decay as an exponential process, where the rate of decay depends on how frequently sound waves strike absorptive surfaces. Working through the physics gives:
Constant = 24 × ln(10) / c
Where c is the speed of sound in air (approximately 343 m/s at 20°C). This gives 24 × 2.303 / 343 ≈ 0.161 for metric units. For imperial units (feet per second, c ≈ 1125 ft/s): 24 × 2.303 / 1125 ≈ 0.049.
The constant is not empirical — it is derived directly from the physics of sound propagation in air at room temperature. Using the wrong constant for your unit system will give a result that is approximately 3.3 times too high (if using the metric constant with imperial inputs) or too low (if using the imperial constant with metric inputs).
What is a Sabin?
A Sabin (named after Wallace Clement Sabine) is the unit of sound absorption. One metric Sabin represents the equivalent absorptive area of one square metre of a perfectly absorptive surface — a surface that absorbs 100% of incident sound energy. A 10 m² wall with absorption coefficient 0.30 contributes 3 Sabins to the total absorption A. Total absorption is the sum of (area × absorption coefficient) for all surfaces in the room.
What is an absorption coefficient?
An absorption coefficient is a dimensionless number between 0 and 1 that expresses what fraction of incident sound energy a material absorbs at a given frequency. A coefficient of 0 means the material reflects all sound (perfect mirror). A coefficient of 1 means it absorbs all sound (perfect absorber). In practice, most real materials have coefficients between these extremes, and the coefficient varies with frequency — most materials absorb high frequencies more effectively than low frequencies.
Acoustic Problems and Solutions
Why does my room sound echoey even after treatment?
The most common causes of persistent echo after acoustic treatment are:
Insufficient low-frequency absorption. Thin acoustic foam and standard acoustic panels are effective at mid and high frequencies but absorb very little below 200–300 Hz. If a room still sounds echoey, it may be experiencing low-frequency buildup (room modes). Bass traps — thick panels or corner placement — are needed for effective low-frequency absorption.
Untreated parallel walls. Hard parallel surfaces facing each other create flutter echo — a rapid, repeating series of reflections that sounds like a metallic ringing or slap. Even one treatment on one wall can significantly reduce flutter echo; treating both walls eliminates it.
Insufficient total coverage. A few panels on one wall may not provide enough total absorption to meaningfully reduce RT60. The Sabine formula shows that A = Σ(S × α) — total absorption depends on both the size and absorptivity of every treated surface, not just the presence of any treatment.
What is flutter echo and how does it differ from reverberation?
Reverberation is the gradual, diffuse decay of sound energy in a room — it decays smoothly and is well described by RT60. Flutter echo is a distinctly different acoustic problem: rapid, repetitive reflections between two parallel reflective surfaces (typically two opposite walls), perceived as a fast ringing or fluttering sound after a sharp transient like a handclap. Flutter echo is not captured by the RT60 metric and is not solved by reducing RT60 — it requires breaking up or treating the specific parallel surfaces creating the reflection path.
What are room modes and do they affect RT60?
Room modes (also called standing waves or eigenmodes) are resonant frequencies that build up inside a room due to reflections between parallel surfaces. They are determined by room dimensions: the lowest axial mode frequency equals c / (2L), where L is the length of the room and c is the speed of sound. Room modes cause certain low frequencies to be emphasised and others to be attenuated depending on listening position. They are a separate phenomenon from RT60 and cannot be predicted or solved by RT60 calculation alone. Room mode problems typically require room dimension changes, room mode trapping, or digital room correction.
About This Website
Who runs Reverb-Calculator.com?
Reverb-Calculator.com is founded and maintained by Noah Bennett, an acoustic engineer and room acoustics educator. Noah Bennett researches and writes all content on the site. The site is independent and not affiliated with any acoustic standards body, architecture firm, or audio equipment manufacturer.
How do I report an error or get in touch?
Use the Contact page. For formula errors, include the input values you used and the result you believe is incorrect. For content errors, include the page URL and the specific claim. All messages are reviewed personally by Noah Bennett.
Last updated: June 2026 — Noah Bennett, Reverb-Calculator.com