It's the time for a sound to decay by 60 decibels after the source stops, computed via the Sabine equation RT60 = 0.161·V/(α·S).

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🔊 Room Acoustics — RT60, Modes & Flutter Echo

Model sound behaviour in rectangular rooms. Adjust dimensions and wall absorption to compute RT60 reverberation time, Schroeder frequency, and axial room modes. Visualise standing wave patterns.

Room Acoustics & Architectural Sound3DEasy60 FPS

About this simulation

This model computes how a rectangular room actually sounds, from its dimensions and wall absorption alone. Sabine's equation turns those inputs into an RT60 reverberation time; the Schroeder frequency marks where the room stops behaving like a set of discrete resonant modes and starts behaving statistically; and the axial mode calculator finds the exact frequencies (like the low bass "boom" in a small room) where standing waves form between opposite walls. Drag the source and listener dots to see the critical distance circle in action, and switch materials to hear — visually — how absorption reshapes the whole response.

🔬 What it shows

A top-down view of the room with animated wave rings spreading from the source, simplified ray-path reflections bouncing off walls, and a critical-distance circle, alongside a simulated frequency response chart with red markers at each axial room mode and a dashed line at the Schroeder frequency.

🎮 How to use

Adjust width, length and height, pick an absorption material preset or set a custom α, toggle ray paths and mode frequency overlay, and drag the source (S) and listener (L) dots in the top view to see RT60, Schroeder frequency, critical distance and the axial mode table update live.

💡 Did you know?

A small bathroom with hard tile walls has a low absorption coefficient (α ≈ 0.02) and can have an RT60 several times longer, relative to its tiny volume, than a much bigger, heavily damped recording studio — which is exactly why singing in the shower sounds so resonant.

Frequently asked questions

What is RT60?

It's the time it takes for a sound to decay by 60 decibels after the source stops — the standard measure of how "live" or "dead" a room sounds. It's computed here from the Sabine equation: RT60 = 0.161·V/(α·S), where V is room volume, S is total surface area and α is the absorption coefficient.

What are axial room modes?

They're resonant standing-wave frequencies that form between a pair of parallel walls, computed as f = (c/2)·(n/L) for each dimension L. Small rooms have their lowest modes at low, audible bass frequencies, which is why small rooms often have an uneven, boomy bass response at specific notes.

What is the Schroeder frequency?

It's the frequency above which room modes are so densely packed and overlapping that the room's response is better described statistically (diffuse reverberant field) than as individual resonances. Below it, individual modes dominate and can be heard as distinct peaks and dips.

What is critical distance?

It's the distance from the sound source at which the direct sound and the reverberant (reflected) sound field are equal in level. Closer than that, direct sound dominates and speech is clearer; further away, reverberation dominates and clarity drops.

Why does absorption material change the sound so much?

Higher absorption (α) means more sound energy is soaked up by walls, floor and furnishings on each reflection, so RT60 drops, the room's response flattens out, and individual axial modes become less pronounced and audible — this is exactly why studios use heavy acoustic treatment.

⚙ Under the hood

Change room size and absorption to see RT60 shift, compare Sabine's estimate, and find room modes below the Schroeder frequency and flutter echo.

room acousticsRT60SabineSchroeder frequencystanding wavesroom modes

3D · Three.js / WebGL renderer · 60 FPS target · runs fully client-side, no install