RT60 (Reverberation Time 60) is the time it takes for sound to decay by 60 decibels after the source stops. It's the standard measurement for room echo. A higher RT60 means more echo; a lower RT60 means a 'drier' sound. For conference rooms, ideal RT60 is typically 0.4-0.6 seconds.

What is a good RT60 for a conference room?

For conference rooms used for video calls and hybrid meetings, aim for RT60 between 0.4 and 0.6 seconds. Below 0.4s can sound unnaturally 'dead.' Above 0.6s, echo starts affecting speech clarity. Above 0.8s, remote participants will struggle to follow conversations.

How is RT60 measured?

RT60 is measured by creating an impulse sound (like a clap or a burst from a speaker), recording the decay, and analyzing how long it takes to drop 60 dB. Since measuring a full 60 dB drop is difficult, T20 or T30 methods measure a smaller range and extrapolate. Professional measurements use calibrated microphones; screening tools like RoomScore use phone microphones with quality checks.

What is the difference between T20 and T30?

T20 and T30 are methods for estimating RT60. T20 measures decay from -5 dB to -25 dB (a 20 dB range) and multiplies by 3. T30 measures from -5 dB to -35 dB (a 30 dB range) and multiplies by 2. T20 is more practical in noisy environments where the decay hits the noise floor before -35 dB.

What is RT60?

RT60 (Reverberation Time 60) is the time it takes for sound to decay by 60 decibels after the source stops. It's the standard measurement for room echo. A conference room with RT60 of 0.5 seconds means sound fades to near-silence in half a second after someone stops speaking. Higher RT60 = more echo. Lower RT60 = less echo.

What RT60 Actually Means

Imagine someone claps their hands in a room. The sound doesn't stop instantly - it bounces off walls, ceiling, and floor, gradually getting quieter with each reflection until it fades to silence.

RT60 measures how long that fade takes. Specifically, it's the time for the sound to drop by 60 decibels (dB). A 60 dB drop means the sound is about one-millionth as loud as when it started - essentially inaudible.

Why does this matter for conference calls?

When someone speaks, their voice bounces around the room before reaching the microphone. If the bounce lasts too long (high RT60), the reflected sound from one syllable overlaps with the next syllable. This makes speech sound muddy and hard to follow - especially for remote participants who only hear what the microphone captures.

In practical terms:

Low RT60 (under 0.5s): Sound dies quickly. Speech is crisp. Room sounds "dry" or "dead."
Medium RT60 (0.5-0.8s): Some natural warmth. Good for most conference rooms.
High RT60 (over 0.8s): Noticeable echo. Speech clarity suffers. Meetings become tiring.

How RT60 is Measured

The basic principle

Create a sudden, loud sound (impulse) - like a clap, a popped balloon, or a burst from a speaker.
Record the decay as the sound bounces around and fades.
Measure how long it takes to drop 60 dB.

T20 and T30: practical measurement methods

In real rooms, measuring a full 60 dB drop is often impractical - background noise (HVAC, traffic) masks the end of the decay before it drops that far. So acousticians use extrapolation:

T20: Measure the decay from -5 dB to -25 dB (20 dB range), then multiply by 3 to estimate full RT60.
T30: Measure from -5 dB to -35 dB (30 dB range), then multiply by 2.

T20 is more practical in noisy environments. T30 is more accurate when background noise is low enough to capture a longer decay.

Professional vs. screening measurements

Professional measurement: Uses calibrated Class 1 microphones, standardized sound sources, and multiple measurement positions. Required for certification and compliance.
Screening measurement: Uses phone microphones with quality checks. Good enough for identifying problem rooms and prioritizing treatment. Not for certification.

How RoomScore measures RT60

RoomScore uses your phone's microphone to capture three claps. It applies a 150 Hz high-pass filter (to reduce HVAC rumble), fits T20 or T30 decay curves when possible (T10 as a fallback), and requires an R^2 fit of at least 0.75 plus SNR/decay checks before reporting results. The final RT60 is selected from the most consistent claps (often the median) and includes a confidence score.

Learn more about RoomScore

What's a Good RT60 for Conference Rooms?

Different spaces have different ideal RT60 values. Concert halls aim for 1.5-2.0 seconds (for musical richness). Recording studios aim for 0.2-0.3 seconds (for precision). Conference rooms fall in between:

RT60	Rating	What to expect
< 0.3s	Very dry	May feel uncomfortably "dead." Rare in offices without heavy treatment.
0.3 - 0.5s	Excellent	Crisp speech, minimal echo. Well-treated rooms.
0.5 - 0.6s	Good	Target range for most conference rooms. Natural sound with controlled echo.
0.6 - 0.8s	Acceptable	Some echo noticeable. Remote participants may need to concentrate.
0.8 - 1.0s	Problematic	Clear echo. Long meetings become fatiguing. Treatment recommended.
> 1.0s	Poor	Significant echo. Speech clarity seriously degraded. Needs treatment.

RoomScore adjusts targets by room volume, so larger rooms can have higher acceptable RT60 values.

How Room Size Affects RT60

Larger rooms naturally have longer RT60 because sound has farther to travel between reflections. This means:

A 0.4s RT60 in a small huddle room (20 m3) is good.
A 0.6s RT60 in a large boardroom (150 m3) is quite good - hard to achieve without treatment.
A 0.8s RT60 in a small room is problematic.
A 0.8s RT60 in a large room can be acceptable but still echoey.

Rule of thumb for conference rooms:

Small (under 30 m3): Target 0.2-0.4s
Medium (30-150 m3): Target 0.4-0.6s
Large (over 150 m3): Target 0.6-0.9s

These targets are for speech intelligibility in video conferencing. Music rehearsal rooms or multi-purpose spaces might have different requirements.

How to Improve RT60

To lower RT60 (reduce echo), add sound-absorbing materials. The relationship is roughly linear: adding absorption reduces RT60 proportionally.

Effective treatments:

Acoustic panels: Fabric-wrapped fiberglass panels absorb 80-95% of sound. Most effective per square meter.
Ceiling treatment: Acoustic ceiling tiles or suspended "clouds" catch sound before it reflects.
Curtains: Heavy curtains on glass walls provide absorption that can be opened when not needed.
Carpet: Thick carpet on hard floors helps, especially for footsteps and chair noise.

How much treatment?

As a rough guide, adding 1 m² of good acoustic panel (NRC 0.8+) to a 50 m³ room might reduce RT60 by about 0.05-0.1 seconds. So if you're at 0.8s and want to reach 0.5s, you might need 3-6 m² of treatment.

Placement matters too. Treating the wall directly behind seating typically has more impact than treating a side wall.

Learn more about fixing conference room echo

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