Most room acoustic problems come down to one number. You don't need to understand absorption coefficients, flutter echo frequencies, or acoustic impedance to meaningfully improve how a room sounds. You need to understand RT60.

RT60 is the single most important acoustic measurement in room design. Once you know your room's RT60, you understand why your speakers sound muddy, why your conference calls are echoey, or why your recording space sounds like a bathroom — and more importantly, what to do about it.

What's the Quick Answer?

RT60 is the time it takes for sound to decay by 60 decibels after the source stops. A low RT60 (under 0.3 seconds) is a "dead" room. A high RT60 (over 2 seconds) is live and reverberant. The ideal depends on the use case: home listening rooms target 0.3–0.5 seconds, conference rooms want under 0.6 seconds, and concert halls are designed for 1.8–2.2 seconds.

Where Does the "60" Come From?

The "60" in RT60 refers to decibels. When a sound source stops, the sound in a room doesn't disappear instantly — it bounces off surfaces and gradually loses energy with each reflection. RT60 measures how many seconds it takes for that energy to fall 60 dB from its peak level.

60 dB was chosen because it represents roughly the dynamic range from a normal conversational voice to the threshold of hearing in a quiet room. In practice, measuring a full 60 dB decay requires a very quiet test environment, so engineers often measure RT20 or RT30 (20 or 30 dB drops) and extrapolate to get RT60.

How Is RT60 Calculated?

The theoretical foundation is Sabine's formula, developed by Wallace Clement Sabine in 1900:

RT60 = 0.161 × V / A

Where:

• V = room volume in cubic meters
• A = total absorption in the room (surface area × absorption coefficient, summed across all surfaces)
• 0.161 = a constant derived from the speed of sound

What this means practically: larger rooms have more air volume for sound to bounce around in, so RT60 increases with room size. More absorptive surfaces reduce RT60. Hard surfaces (concrete, glass, tile) have absorption coefficients near 0 and contribute almost nothing. Soft surfaces (carpet, acoustic foam, heavy curtains) have coefficients from 0.3 to near 1.0 and absorb significant energy.

For non-uniform rooms — which is almost every real room — the Eyring formula is more accurate than Sabine's. But Sabine's gives a reasonable first estimate and is easier to calculate by hand.

How Do You Measure RT60 in Practice?

You don't need professional acoustic measurement equipment. Three approaches in increasing order of accuracy:

Method 1 — Impulse response measurement (free, accurate). Use the free app Room EQ Wizard (REW) on a laptop connected to a measurement microphone. REW generates a test signal, captures the room's response, and calculates RT60 automatically. A USB measurement microphone like the MiniDSP UMIK-1 costs about $75. This is the standard method for home studio and home theater optimization.

Method 2 — Impulse source (easy, less precise). Clap sharply, snap a balloon, or strike a sharp impulse in the room. Use any recorder to capture the decay. Measure how long the noise tail takes to fade out. This gives a usable ballpark RT60 for mid-frequencies but doesn't capture frequency-specific decay rates.

Method 3 — Estimate from Sabine. If you know your room's volume and can estimate the surface materials, calculate RT60 directly from the formula. Absorption coefficient tables for common materials are widely available online. Useful for planning before you measure anything.

Measure in multiple positions. RT60 varies across a room, especially in spaces with non-parallel walls or mixed surface materials. Averaging several measurement positions gives a more representative number than a single point.

What RT60 Values Mean

| RT60 | Character | Good for… | |------|-----------|-----------| | < 0.2 s | Very dead | Anechoic testing, broadcast voiceover | | 0.2–0.4 s | Dry | Recording studio vocal booths, podcast studios | | 0.3–0.5 s | Controlled | Home listening rooms, home recording | | 0.4–0.6 s | Natural | Conference rooms, office spaces | | 0.6–1.0 s | Live | Live music rooms, larger home theaters | | 1.0–1.5 s | Reverberant | Small performance venues | | > 2.0 s | Very live | Large churches, concert halls |

There is no universally correct RT60. A recording studio vocal booth at 0.6 seconds sounds horribly reverberant. A cathedral at 0.4 seconds sounds dead and lifeless. Match the RT60 to the use case.

How RT60 Affects Different Applications

Home listening rooms

For two-channel stereo and home theater, the target RT60 is 0.3–0.5 seconds. Too short and the room sounds unnatural — music loses its sense of space. Too long and bass frequencies accumulate into muddy low-end, and stereo imaging becomes vague.

Most untreated living rooms measure 0.5–0.8 seconds, which is within an acceptable range but on the high side. The main problem in typical rooms isn't overall RT60 — it's uneven RT60 across frequencies. Bass decays more slowly than midrange in most rooms, which is why bass sounds boomy even when everything else sounds reasonably clear.

Recording studios

Recording requires low RT60 in isolation rooms where tracks are captured (0.2–0.4 seconds for vocals and acoustic instruments) and controlled RT60 in control rooms where mixing happens (0.3–0.4 seconds, flat across frequencies). A control room that sounds accurate at 0.35 seconds tells the mixer what's actually on the recording. One at 0.7 seconds colors the sound and leads to mix decisions that don't translate to other playback environments.

Conference rooms and speech spaces

Speech intelligibility drops sharply above RT60 of 0.8 seconds. At 0.6 seconds, speech is still very clear. At 1.0 second, it becomes fatiguing to follow. At 1.5 seconds and above, it becomes genuinely difficult to understand in a noisy room.

This is why conference rooms with hard surfaces and no treatment produce such poor audio quality: their RT60 typically runs 0.8–1.5 seconds, right in the range where speech clarity degrades. See our article on improving speech clarity in conference rooms for specific treatment approaches.

Churches and performance spaces

Spaces designed primarily for music often target RT60 values that would be unacceptable in a speech environment. A large concert hall at 1.8–2.2 seconds RT60 sounds magnificent for orchestral music. A stone church at 3–4 seconds has a distinctive acoustic character that worshippers associate with the space. The challenge comes when these spaces are also used for spoken word — and that's where the conflict between architectural RT60 and speech intelligibility becomes significant.

How Do You Reduce RT60?

RT60 is reduced by adding absorption to the room. More absorption equals shorter RT60. The practical toolkit:

Soft furnishings. Carpet, upholstered furniture, curtains, and cushions all absorb sound. A furnished room has meaningfully lower RT60 than the same room empty. This is why a hotel conference room sounds better with people and chairs in it.

Acoustic panels. Panels made from rigid mineral wool (Rockwool 60, Owens Corning 703) or specialized acoustic foam absorb mid and high frequencies effectively. 2-inch panels work well from about 500 Hz upward. For lower frequencies, you need thicker material — 4 inches or more — or purpose-built bass traps. Our guide to acoustic treatment on a budget covers practical options starting under $100.

Bass traps. Bass frequencies (below 250 Hz) have long wavelengths and require significant absorber thickness to treat effectively. Bass traps placed in room corners — where bass energy concentrates — are the most efficient way to reduce low-frequency RT60. In most untreated rooms, this is where the biggest improvement per dollar comes from.

Diffusion. Diffusers don't reduce overall RT60 — they scatter reflections and soften the harshness of early reflections without making the room dead. Use them on the rear wall of a listening room when you want some acoustic liveliness without adding reverb.

RT60 Varies With Frequency

One of the most important concepts to understand: RT60 is not a single number for your room. It varies with frequency. Sabine's formula gives an average, but most rooms have dramatically longer RT60 in the bass than in the midrange.

A typical untreated room might measure:

| Frequency | RT60 | |-----------|------| | 125 Hz | 0.9 s | | 250 Hz | 0.7 s | | 500 Hz | 0.5 s | | 1000 Hz | 0.4 s | | 2000 Hz | 0.4 s | | 4000 Hz | 0.35 s |

This is why bass sounds boomy even when the room sounds reasonably okay for voices — the bass RT60 is roughly double the midrange RT60. Flattening the RT60 curve across frequencies — not just reducing the average — is the central challenge in room acoustic design.

Professional room treatment starts with broadband measurement, identifies where the RT60 curve peaks, and addresses those frequencies first. In most rooms, that means bass trapping before anything else.

The Relationship Between RT60 and Room Size

Larger rooms naturally have higher RT60 because sound has more space to bounce before it's absorbed. A small home recording booth can be treated to 0.2 seconds without difficulty. Treating a 500-seat concert hall to 0.4 seconds would require covering every surface in thick absorptive material — which would destroy the acoustic character of the space entirely.

This is why acoustic design scales differently by room size. The same amount of treatment that dramatically reduces RT60 in a small room has almost no measurable effect in a large one. Room volume is the primary constraint on how low RT60 can realistically go.

For practical room acoustic planning, use the online speaker placement calculator to understand how your room's dimensions interact with speaker placement before committing to treatment. Room dimensions affect bass modes (standing waves) as well as RT60, and treating one without considering the other produces incomplete results.

For a broader overview of how RT60 fits into room acoustic design, see our complete guide to speaker placement and the article on why rooms echo and how to fix it. If your room's problems are primarily bass-related, the frequency-specific RT60 analysis above is the right starting point for treatment planning.