RT60 explained simply
The RT60 is one of the most important values when assessing room acoustics. Simply put, it describes how long sound lingers in a room.
An appropriate reverberation time ensures that speech is intelligible, music is clear, and a room does not sound too echoey or too dry.
But what does RT60 actually mean, how is it measured, and what value is sensible for your room?
What does RT60 mean?
RT60 stands for Reverberation Time 60 or reverberation time 60.
The value indicates how long it takes for a sound level to decrease by 60 decibels after the sound source has been turned off.
An example:
If a loud noise is produced in a room and it noticeably diminishes after approximately 0,5 seconds, the reverberation time is approximately 0,5 seconds.
The higher the RT60 value, the longer the room reverberates.
The lower the value, the quicker the sound is dampened in the room.
Why is reverberation time important?
Reverberation time strongly influences how we perceive a room.
If it is too long, speech, music, and individual sound events can blur together. The room sounds echoey and imprecise.
If the reverberation time is too short, the room can sound dry, small, or unnatural.
A balanced RT60 improves, among other things:
- Speech intelligibility
- Clarity of music
- Location of individual sound sources
- Concentration in offices
- Recording quality in the studio
- Listening comfort in living and working spaces
The ideal reverberation time always depends on the use and size of the room.
What does a too long RT60 sound like?
A too long reverberation time often manifests through the following characteristics:
- Speech sounds unclear
- Conversations become exhausting
- Music sounds blurred
- the bass sounds slow and booming
- individual tones overlap
- the room sounds loud and restless
- Clapping produces a long reverberation
Especially in rooms with many hard surfaces, long reverberation times often occur.
Typical causes are:
- Concrete walls
- Glass surfaces
- Tiled or stone floors
- Empty walls
- High ceilings
- Few furnishings
- Lack of acoustic elements
Can an RT60 also be too short?
Yes. A room can also be overly dampened.
If too many absorbing materials are used, the room can sound lifeless and unnatural. Music loses its spatial quality, and voices may sound very close and dry.
Especially in recording rooms and music rooms, the lowest RT60 value is not automatically the best.
The goal is a uniform reverberation time that suits the intended use.
Which RT60 is good?
There is no single RT60 value that is ideal for all rooms.
The appropriate reverberation time depends on several factors:
- Room size
- Room volume
- Use
- Furnishings
- Desired sound
- Frequency range
- Number of people in the room
As a rough guide, the following ranges can be used:
| Room type | Typical RT60 range |
|---|---|
| Studio control room | approx. 0,2 to 0,4 seconds |
| small recording room | approx. 0,3 to 0,6 seconds |
| podcast or speech room | approx. 0,2 to 0,4 seconds |
| living space | approx. 0,4 to 0,8 seconds |
| office or meeting room | approx. 0,4 to 0,7 seconds |
| classroom | approx. 0,5 to 0,8 seconds |
| concert hall | often significantly over 1 second |
These figures are only guidelines. A large room generally requires a longer reverberation time than a small room.
The intended use also plays an important role. A room for speech recordings is usually tuned drier than a concert hall.
Is RT60 the same at all frequencies?
No. Reverberation time is considered across different frequency ranges.
A room may sound dry in the high frequencies while low frequencies still resonate for a long time.
Therefore, RT60 should not only be assessed as a single average value.
The distribution across the entire frequency range is important.
Typical problems are:
- long reverberation time in the bass
- too much damping in the high frequencies
- uneven values between frequencies
- individual particularly long decaying areas
Good room acoustics mean not only a short reverberation time but also a controlled and even decay.
RT60 and bass problems
Low frequencies require particularly long times to decay.
Therefore, many small rooms show significantly longer decay times in the bass range than in the mids and highs.
This can lead to the bass being perceived as:
- boomy
- imprecise
- slow
- overemphasised
- poorly localisable.
Normal thin acoustic panels help against low frequencies only to a limited extent. For better control, thick broadband absorbers, bass traps, and optimised speaker positioning are often required.
How is RT60 measured?
Reverberation time can be measured with a measurement microphone and acoustic software.
A commonly used free software is
Room EQ Wizard , abbreviated REW.For a measurement, the following are usually required:
a calibrated measurement microphone
- a computer
- an appropriate audio connection
- a loudspeaker
- measurement software like REW
- The software generates a test signal and analyses how sound decays in the room.
Subsequently, the reverberation times for different frequency ranges are displayed.
What do T20 and T30 mean?
In small rooms, the sound level often cannot be measured cleanly over the full range of 60 decibels.
Therefore, measurement programs often use values like T20 or T30.
With T20, a smaller decay range is evaluated and then extrapolated to 60 decibels.
With T30, a range of 30 decibels is used and also converted to RT60.
T20 and T30 are therefore not reverberation times of only [[NUM]] or [[NUM]] seconds. They are different measurement methods for calculating the theoretical RT60.
RT60 or EDT?
In addition to RT60, EDT is often displayed.
EDT means
Early Decay Time and describes the early decay of sound. This value can be particularly important because the first part of the reverberation strongly influences our subjective perception.
A room can have an acceptable RT60 in measurement terms and still be perceived as echoey if the early reflections are particularly strong.
Therefore, RT60, EDT, and other measurement values should always be considered together.
How can RT60 be improved?
A too long reverberation time can be reduced by absorbing surfaces.
Suitable measures include:
broadband absorbers on the walls
- heavy curtains
- Ceiling Cloud
- Bass traps in the room corners
- carpets
- upholstered furniture
- acoustically effective partitions
- wall and ceiling absorbers
- The room should not only be treated in the high frequencies.
Thin materials often absorb mainly high frequencies. The bass can therefore remain uncontrolled, while the room can simultaneously sound dull.
For a balanced acoustics, sufficiently thick absorbers should therefore be used.
Where should absorbers be placed?
The correct position depends on the use of the room.
In a recording studio, the following areas are often treated:
First reflection points on the side walls
- Ceiling above the listening position
- Room corners
- partially the front wall
- Rear Wall
- In offices or meeting rooms, wall absorbers and Ceiling Clouds can significantly improve speech intelligibility.
In living spaces, decorative acoustic pictures, Ceiling Clouds, or custom-made absorbers are often used.
Why a single RT60 number is not enough
Room acoustics should not be assessed based on a single value.
Two rooms can have the same average RT60 value and still sound completely different.
In addition to reverberation time, the following measurements should also be considered:
Impulse response
- Frequency Response
- early reflections
- Waterfall diagram
- Spectrogram
- Bass decay time
- ETC diagram
- Only the combination of various measurement values allows for a reliable assessment.
Common mistakes in RT60 optimisation
Only use thin acoustic panels
Thin panels mainly reduce high frequencies. The bass range often remains virtually unchanged.
Fully dampen the room
Too much absorption can make the room sound unnaturally dry and lifeless.
Use only one measurement point
A single measurement point does not reliably represent the entire acoustics of a room.
Focus only on the average value
A low average value does not automatically mean good acoustics. Individual frequencies can still resonate for a very long time.
Equate furniture with professional absorbers
Sofas, carpets, and curtains mainly help in certain frequency ranges. They do not replace a deliberately planned acoustic treatment.
RT60 describes how long sound lingers in a room. It is an important measurement for recording studios, offices, home cinemas, music rooms, and living spaces.
Conclusion
A good reverberation time should match the use of the room and be as uniform as possible across the various frequencies.
A very low RT60 value is not automatically better. What matters is a balanced room that sounds clear, controlled, and still natural.
Professionally measuring room acoustics
Do you want to know if the reverberation time in your room is too high, too low, or unbalanced?
Rock Tribe Audio supports you with professional room measurement, evaluation, and acoustic optimisation of recording studios, music rooms, home cinemas, offices, and living spaces.
Based on precise measurements, we develop an individual solution using broadband absorbers, bass traps, Ceiling Clouds, and diffusers.
Measure reverberation time now and improve room acoustics
Frequently asked questions about RT60
RT60 describes the time it takes for sound to drop by 60 decibels after the sound source has been turned off.
What does RT60 mean?
Is a low RT60 always better?
No. A too low reverberation time can make a room sound dry and lifeless. The optimal RT60 depends on the use and size of the room.
What RT60 is good for a recording studio?
In small control rooms, the reverberation time often lies between [[NUM]] and [[NUM]] seconds. However, the ideal value depends on the room volume and studio concept.
How can I measure RT60?
RT60 can be measured with a calibrated measurement microphone and software like Room EQ Wizard.
What is the difference between RT60 and T30?
RT60 describes the theoretical decay time of [[NUM]] decibels. T30 measures a smaller level range and extrapolates the result to [[NUM]] decibels.
Why is RT60 often longer in the bass?
Low frequencies are less strongly absorbed by walls and thin absorbers. They also excite room modes that cause the bass to resonate longer.
Do carpets help against a long RT60?
Carpets mainly absorb high frequencies. They hardly help with long decay times in the bass.
Can RT60 be reduced with diffusers?
Diffusers distribute sound but absorb it only to a limited extent. To significantly reduce reverberation time, mainly absorbers are used.
Diffusoren verteilen Schall, absorbieren ihn aber nur begrenzt. Zur deutlichen Reduzierung der Nachhallzeit werden hauptsächlich Absorber eingesetzt.
