RT60 is the time it takes for sound to decay by 60 decibels in a room—a standard measurement of how “live” or “dead” an acoustic space is. If you clap your hands in a bare room and count how long the sound takes to fade away almost completely, you’re observing RT60 in action.
Understanding RT60 is fundamental if you record audio, mix music, or design a listening space. Too much RT60 and your room becomes muddy and echoey. Too little and it feels dead and unnatural. Getting RT60 right is what separates a professional-sounding studio from a frustrating recording environment.
What RT60 Measures
RT60, short for reverberation time, is a metric that quantifies how much sound decays in a room over time. Specifically, it measures the number of seconds it takes for the sound level to drop 60 decibels from its original intensity.
A decibel is a logarithmic unit of sound intensity. 60 dB is a perceptually significant drop—it’s roughly the difference between normal speech and a whisper. When sound drops 60 dB, it’s considered to have essentially decayed away for practical purposes.
The measurement is named after Wallace Clement Sabine, an American physicist who pioneered acoustic science in the late 1800s. Sabine worked on the Boston Symphony Hall and developed the mathematical relationship between room size, surface absorption, and reverb time. His work established RT60 as the industry standard for measuring room acoustics.
Why RT60 Matters
Every room has an RT60. Some rooms—like a concert hall or large cathedral—have a long RT60 of 2 to 3+ seconds or more. Others, like a small carpeted office or a vocal booth with heavy acoustic treatment, might have an RT60 of 0.3 to 0.5 seconds.
The RT60 of your space directly affects how your recordings and mixes will sound. If you record a vocal in a room with a 2-second RT60, the reverb will muddy the vocal, making it harder to hear clarity and diction. If you record in an over-treated space with a 0.2-second RT60, the vocal might sound dead and unnatural—missing the slight warmth that a small amount of room reflections provides.
For mixing, knowing your room’s RT60 helps you understand what you’re hearing. If your mixing room has a long RT60, you might be adding too much reverb to your mix because the room is already adding reverb. When you listen to your mix in a car or on headphones, it sounds over-reverbed.
For acoustic design and treatment, RT60 is the key metric. When you plan acoustic panels, bass traps, or diffusers, you’re aiming to achieve a target RT60 that’s appropriate for your room’s use—tighter for recording, slightly longer for monitoring.
RT60 Values Across Different Room Types
Different rooms have different ideal RT60 values depending on their purpose:
A vocal booth or small recording space typically aims for an RT60 of 0.3 to 0.5 seconds. This is quite dry—reflections decay quickly so recordings capture the source with minimal room character. It’s ideal for recording spoken word, vocals, or acoustic instruments where you want clarity and control.
A small home studio or project studio often targets an RT60 of 0.5 to 0.8 seconds. This provides enough decay to avoid a dead, lifeless feel, while keeping reflections controlled enough for clean mixing.
A medium listening room (like a mastering suite or professional mixing room) might aim for 0.8 to 1.2 seconds. This creates a balanced acoustic environment where you can hear reverb on recordings without the room’s own reverb coloring your perception.
A large control room (common in commercial studios) might target 1 to 1.5 seconds. The larger volume allows for longer RT60 while still maintaining clarity and a balanced stereo image.
A concert hall or performance space typically has an RT60 of 1.5 to 3+ seconds or longer. This reverberation enhances the sound of acoustic instruments, orchestras, and singing. A hall with an RT60 under 1.5 seconds sounds too dry for classical music; one over 3 seconds can sound muddy.
These are guidelines, not absolutes. The ideal RT60 for a space depends on what you’re doing and personal preference. Use the RT60 calculator to measure your own room and see where it falls.
How RT60 Is Calculated: The Sabine Formula
The most common way to estimate RT60 is using the Sabine formula, named after Wallace Clement Sabine:
RT60 = 0.161 × V / A
Where:
- V is the room volume in cubic meters
- A is the total absorption in sabins (a unit of sound absorption)
- 0.161 is a constant that accounts for the speed of sound and the 60 dB decay threshold
To use this formula, you need to know your room’s dimensions (to calculate volume) and the absorption coefficients of all your surfaces—walls, floor, ceiling, and any furnishings or acoustic treatment. Each material has a different absorption coefficient, which tells you how much sound it absorbs across different frequencies.
For example, if you have a room that’s 4 m × 5 m × 3 m tall (60 m³ volume), with untreated drywall walls and a carpet, the total absorption might be around 12 sabins. Using the Sabine formula: RT60 = 0.161 × 60 / 12 = 0.81 seconds. This gives you a rough estimate of the room’s reverberation time.
In practice, most people use a calculator tool rather than working through the math by hand. The formula assumes that sound decays evenly across the frequency spectrum, which isn’t always true in real rooms—but it’s a solid starting point. See detailed information on the Sabine formula and how to apply it accurately.
There’s also the Eyring formula, which refines the Sabine estimate when absorption coefficients are high (above about 20% of the room surface). The Eyring formula accounts for the fact that high-absorption rooms don’t always follow Sabine’s linear relationship perfectly.
Using RT60 to Improve Your Room
Once you know your room’s RT60, you can adjust it if needed using acoustic treatment. Different materials absorb sound at different rates:
Soft, porous materials like foam, fiberglass, and mineral wool are good broadband absorbers. They work across a wide frequency range and reduce RT60 noticeably.
Bass traps are specialized absorbers for low frequencies. Because long wavelengths (low frequencies) reflect and resonate in rooms, they need dedicated treatment. Bass traps placed in corners or along walls catch these reflections and reduce boomy, muddy lows.
Diffusers scatter sound reflections rather than absorbing them. Instead of killing reverb, diffusers break up standing waves and reflections so the room feels less echoey without becoming dead.
Hard, reflective materials like glass and drywall don’t absorb much sound—they reflect it, which increases RT60. If your room is too dead (RT60 too short), you might need to reduce treatment or add reflective surfaces back.
The goal is usually to achieve an RT60 that’s balanced and appropriate for your application. Learn which acoustic treatment options work best for lowering RT60 in your specific space.
Frequently Asked Questions
Can I measure RT60 myself without expensive equipment?
Yes, approximately. You can clap sharply and time how long the sound takes to fade, or use a free app that measures sound level on a smartphone. These give you a rough estimate. For precise measurement, you’d need an audio interface, a measurement microphone, and acoustics software that generates an impulse response and analyzes the decay—but the DIY method works for getting in the ballpark.
Is a longer RT60 always worse?
Not necessarily. A concert hall with a 2.5-second RT60 sounds wonderful for orchestral music. The issue is matching RT60 to the room’s purpose. For recording speech or clear vocal takes, long RT60 is problematic. For listening to music in a home theater, a slightly longer RT60 (around 1.2–1.5 seconds) can sound great. The problem arises when RT60 is mismatched to the task—recording vocals in a reverberant space, or trying to mix in a dead room.
How often does RT60 change?
It changes whenever you change the room’s contents. Adding furniture, curtains, people, or acoustic panels all absorb sound and lower RT60. An empty room and a furnished room have different RT60 values. Temperature and humidity can also affect RT60, though the effect is usually small in normal indoor conditions.
Why does the Sabine formula sometimes not match my measured RT60?
The Sabine formula is an estimate. It assumes sound decays uniformly across frequencies and throughout the room, which isn’t always true. Real rooms have room modes (resonances at certain frequencies) and non-uniform absorption. For a more accurate prediction, you’d measure impulse responses at different frequencies or use acoustic simulation software.