Introduction
Every room has a acoustic signature, and that signature either serves your production or fights it. Reverberation time, measured as RT60, is the single most important metric for evaluating whether a space is suitable for dialogue recording, ADR sessions, foley work, or music capture. RT60 measures how long it takes for sound to decay by 60 decibels after the source stops. A well-treated ADR booth sits between 0.1 and 0.3 seconds. A live scoring stage might run 0.8 to 1.2 seconds. A concert hall designed for orchestral music operates between 1.5 and 2.5 seconds. Recording in a space with the wrong RT60 forces you into expensive remediation in post, or worse, forces a reshoot. This RT60 calculator uses the Sabine equation to predict reverberation time across six frequency bands based on room dimensions and surface materials, so you can evaluate any space before committing to it.
What This Tool Calculates
Location sound mixers evaluate hundreds of potential recording spaces throughout a career. The ones who deliver the cleanest tracks share a discipline: they measure or estimate RT60 before they roll. A room that looks acoustically dead might have a hard floor, plaster ceiling, and glass walls that create a 1.8-second tail at mid frequencies. A room that sounds live in conversation might actually be acceptable for production sound because the reverb character falls in the upper frequency range, where post-production noise reduction works most effectively. Knowing the RT60 at 500 Hz and 1 kHz tells you what kind of sound you will capture on the close mic and whether the room ambience will survive dialogue editing and mixing. A 0.5-second RT60 at 1 kHz is generally workable on a close-positioned boom. Anything above 0.8 seconds starts creating problems that follow you through the entire post-production pipeline.
The Formula and How It Works
Wallace Clement Sabine derived the fundamental equation for room reverberation in 1900, and it remains the standard for acoustic prediction. The formula is RT60 equals 0.161 multiplied by room volume in cubic meters, divided by total absorption in sabins. Total absorption equals the sum of each surface area multiplied by its absorption coefficient at the frequency of interest. Absorption coefficients range from near zero for hard reflective surfaces like concrete and glass to near one for highly absorptive materials like studio foam and heavy carpet. The 0.161 constant derives from the relationship between the speed of sound, the natural logarithm base, and the definition of the decibel scale. For rooms where the average absorption coefficient exceeds approximately 0.25, the Eyring equation provides better accuracy because Sabine's equation overestimates RT60 in heavily treated spaces.
Real-World Examples
Three Real Production Scenarios
Scenario one: you are evaluating a hotel conference room for an interview shoot. The room is 8 by 6 by 2.8 meters with carpet, drop ceiling, and one glass window wall. Entering those values shows an RT60 of approximately 0.45 seconds at 1 kHz, well within acceptable range for close-mic production sound. Scenario two: you are considering a warehouse for a music video shoot that also requires dialogue. Concrete floor, bare brick walls, and a metal roof give an RT60 above 2.5 seconds, making clean dialogue recording impossible without extensive acoustic treatment. Scenario three: you are building a voiceover booth in a spare room. The calculator helps you determine how much acoustic foam you need to bring the RT60 below 0.25 seconds, and shows the frequency-dependent effect of each material choice so you can treat low-frequency buildup with bass traps and high-frequency energy with broadband panels.
Ideal RT60 Targets by Space Type
| Detail | Value |
|---|---|
| Recording studios for voice and dialogue work best between 0.2 and 0.4 seconds. | |
| This range keeps the room from sounding clinically dead while avoiding audible smear on consonants and transients. | |
| ADR booths need to be even drier, ideally 0.1 to 0.3 seconds, because any room character in the booth competes with the production sound ambience you are trying to match. | |
| Music recording rooms vary widely by instrument. | |
| Drum rooms often target 0.4 to 0.6 seconds. |
Pro Tips and Common Mistakes
Pro Tips
- Absorption is not uniform across the frequency spectrum.
- This is why RT60 must be evaluated across multiple frequency bands rather than a single number.
- Low frequencies below 250 Hz are the hardest to control and require mass-loaded barriers or tuned resonant absorbers.
- Standard acoustic foam with 2-inch depth absorbs well above 500 Hz but contributes almost nothing at 125 Hz.
Common Mistakes
- Start your treatment at the first and second reflection points, not the corners.
- The floor behind the desk, the ceiling above the mix position, and the side walls at ear height are where early reflections smear the stereo image and blur transients.
- Corner loading is the second priority because bass frequencies build up at room boundaries.
Frequently Asked Questions
What is a good RT60 for a recording studio?
For voice recording and dialogue, target 0.2 to 0.4 seconds at 500 Hz to 1 kHz. For music rooms, the target depends on the instruments being recorded. String and piano rooms work at 0.5 to 0.8 seconds. Scoring stages for full orchestras are designed for 0.8 to 1.2 seconds.
Is the Sabine equation accurate?
The Sabine equation is accurate for rooms with low to moderate absorption where the average absorption coefficient is below about 0.25. For highly treated rooms, the Eyring equation provides better accuracy. Both equations assume uniform absorption distribution, which is rarely perfectly true in practice. Real-world measurements will vary from predictions based on actual construction tolerances and furniture.
How do I measure RT60 in an actual room?
The standard method uses an omnidirectional measurement microphone, a calibrated sound source (balloon burst, starter pistol, or loudspeaker sweep), and acoustic analysis software such as Room EQ Wizard (REW), which is free. The software generates an impulse response and calculates RT60 at each frequency from the decay curve.
Why is RT60 different at different frequencies?
Different materials absorb sound differently at different frequencies. Low frequencies require much more material depth or mass to absorb because of their long wavelengths. A 2-inch acoustic panel absorbs well above 500 Hz but has minimal effect at 125 Hz. This is why broadband acoustic treatment requires a combination of thick panels, bass traps, and resonant absorbers.
Start Calculating
The most common mistake is evaluating a room only at 1 kHz and ignoring the low-frequency behavior. A room can measure acceptably at 1 kHz while exhibiting 2 seconds of reverb at 125 Hz, which affects bass instruments, kick drum, and male voice fundamentals severely. The second mistake is using RT60 as the only metric. Flutter echo, standing waves, and comb filtering from parallel surfaces are not captured in a single RT60 measurement but severely degrade recording quality. Clapping hands and listening for a metallic ringing indicates flutter echo between parallel walls. The third mistake is overloading a room with absorption. Too much treatment creates recordings that sound unnatural when played back in a normal listening environment, because the human brain expects a small amount of room ambience in every recorded source.
