What is RT60?

RT60 is a traditional metric used to measure reverberation time, specifically, how long it takes for sound energy to decay by 60 decibels after a sound source stops. While it is often viewed as a dead-room goal, we treat RT60 as a clarity metric. In large rooms such as concert halls, managing long decay times is essential for speech intelligibility and musical detail. However, in recording studios and smaller listening spaces, the raw number matters less than balance across the frequency range, with more similar RT60 times across all the audio frequencies. Using acoustic treatment to achieve consistent decay, where low-frequency resonances don’t linger longer than the highs, is the key to a trustworthy listening environment, greater clarity, and better sound quality.

What is RT60 and How it Affects What We Hear

In plain language, RT60 measures the hang time of a room. When a loudspeaker or a person speaks, the sound waves don't just vanish instantly when the source stops; they bounce off reflective surfaces until they run out of energy. The room keeps talking after the speakers stop.

RT60 stands for Reverberation Time 60dB. It is the time, measured in seconds, that it takes for the sound pressure level to drop by 60dB. If you’ve ever clapped your hands in a gymnasium and heard that long, metallic zing that lasts for several seconds, you are hearing a long reverb time.

The perceptual impact of this is significant. Excessive reverberation smears the details of music and makes speech difficult to understand because the tail of the previous syllable overlaps the start of the next one. Conversely, a room with an RT60 that is too low can feel oppressive and too clinical, especially if it is unbalanced with too much treble absorption and not enough bass trapping or diffusion. Our goal is never to kill the room, but to control the sound decay so you can hear the original signal without the room’s interference. 

How RT60 is Measured in Real Rooms

RT60 is a measured metric, not a guess. While early pioneers like Wallace Sabine developed a formula to predict reverberation time based on a room’s size and total absorption, real-world complexity usually requires physical testing.

RT60 Measurement Methods

Professionals typically measure reverberation time using one of three methods:

• Sweep signals provide a detailed look at how the room behaves across different frequencies.

• Impulse responses, such as a starter pistol or a balloon pop.

• Noise-based methods, like pink noise played through an omnidirectional speaker, and then cut abruptly.

Standards and Metrics Used

For those who want to dive into the technicalities, ISO 3382-1 is the international standard for these measurements. It ensures that when we talk about acoustic performance, we are using a consistent yardstick. While a simple sound-level meter can show you the volume, specialized software is required to map the decay curve across octave bands accurately.

In a practical way, we can test RT60 across the frequency spectrum using a test mic and software like Room EQ Wizard, to generate a graph like this:

The overall response curve shown here, with drastically longer RT60 times in the bass range, is very common in most rooms, especially smaller, untreated rooms.

Ideal RT60 Depends on the Room and its Purpose

There is no one-size-fits-all RT60. The ideal RT60 is a range determined by what you intend to do in the space.

• Small and Medium Rooms: In a home theater or a small studio, we generally look for a lower RT60 to ensure imaging and clarity. If it’s much higher, intelligibility suffers.

• Large and Performance Spaces: A conference room might need a moderate RT60 for comfortable speech, while a concert hall might have a longer reverberation time to support orchestral music.

The most important tool for getting RT60 under control is absorption. It is the most cost-effective treatment per square foot. For larger rooms, we’ll need sufficient coverage with broadband acoustic panels and other absorbing materials to both reduce RT60 values and make them more consistent across frequencies. 

Why Long RT60 Hurts Clarity (and When it’s Intentional)

In a concert hall, a long reverberation time is often intentional because it adds a good-sounding ambiance to a choral or orchestral performance. But in a room designed for critical listening or recording, that same decay is a problem, reducing intelligibility.

It’s important to distinguish between echo and reverberation. An echo is a distinct reflection, whereas reverberation is the dense collection of reflections that creates a persistent wash of sound. Both are influenced by materials such as glass and drywall, which reflect sound energy into the room rather than dissipating it.

Frequency Matters: Why RT60 isn’t One Number

One of the most dangerous oversimplifications in room acoustics is treating RT60 as a single average number. In the real world, rooms don't decay evenly.

Low frequencies have much longer wavelengths and contain more energy, meaning they tend to linger much longer than high frequencies. This is why a room can feel muddy even if it has plenty of thin acoustic treatment on the walls. If your high-frequency RT60 is short but your low-frequency RT60 is long, the room is imbalanced.

The GIK Perspective: Acoustics is fundamentally a time problem. Frequency response shows what exists, but time response explains why it sounds wrong. Spectrograms give us the most information in a single graph, but RT60 is still a valuable index for understanding how a room actually sounds. 

How Absorbers Reduce RT60 without Killing the Room

The typical mistake is applying thin absorption everywhere. Thin panels are efficient at stopping high-frequency reflections but do nothing for the bass. This leads to a room that sounds lifeless in the treble but remains muddy in the bass.

The Role of Broadband Control

To correct and adjust RT60, we use broadband absorption. Thickness equals bandwidth. A thicker panel or a deep bass trap doesn't just remove bass; it reduces the ringing and decay time of those lower frequencies, bringing them into balance with the rest of the spectrum.

Hybrid Devices: The Best of Both Worlds

To avoid over-absorbing the high frequencies, we use hybrid devices.

• Amplitude Series: These use decorative plates in front of broadband absorbers for diffusion performance while still providing absorption. Thicker devices extend performance further into the bass range, resulting in a wonderfully balanced overall panel. 

• SlatFusor: These prioritize aesthetics, featuring the very popular vertical wood slats, while providing a balance of absorption and scattering.

Measuring and Adjusting RT60 in Practice

If you want to improve your room, follow this workflow: measurement, treatment, and re-measurement.

Don't rely on DIY myths; focus on iterative improvement. Remember: Space is the currency of low-frequency control. There is no shortcut around physics; if you want to control deep sound decay, you need deep treatment. For most rooms, this points to 4” thick broadband devices as a practical minimum to fully address the range of the human voice. Thicker panels will deliver even better low-frequency performance. 

Final Takeaway: Clearer Rooms Sound Better Than Dead Ones

A dead room is rarely the goal; balance is. The objective is clarity, intelligibility, and a natural sound. This is achieved by ensuring your decay times are consistent from the lowest bass notes to the highest treble shimmers. When the room stops talking at the same time the speaker does, you can finally trust what you are hearing.

Get Expert Help Dialing In Your RT60

Every room has a unique voice dictated by its dimensions and materials. At GIK Acoustics, we don't just sell acoustic devices; we provide the expertise to help you reach a trustworthy listening environment.

If you're unsure where to start or how to interpret your room's measurements, we are here to help. You can initiate a free Acoustic Consultation by filling out an Acoustic Advice Form.