What is the critical distance formula for a room?

Dc = 0.057 × √(Q × V / RT60), with V in m³, RT60 in seconds, Q the source directivity factor, and Dc returned in metres.

Which Q value do I use for a corner-mounted source?

Q = 8 for a corner, Q = 4 on an edge, Q = 2 against a wall, and Q = 1 for free space.

What happens if I enter an RT60 of zero?

The tool rejects any RT60 of zero or below and shows an error — RT60 is a divisor in Dc = 0.057 × √(Q × V / RT60), so the value is undefined.

Does doubling the room volume double the critical distance?

No — V sits under the square root, so doubling the volume multiplies Dc by √2, about 1.41.

Acoustic Critical Distance Calculator

Room volume, m³

RT60 reverberation time, s

Source placement

Dc = N/A

Understand Critical Distance

Acoustic engineers need to know the room-radius boundary where the direct sound from a source and the reverberant sound field are equal in level. This crucial measurement is known as the critical distance (Dc), and it dictates the clarity and intelligibility of sound within an enclosed space. This page applies the formula Dc = 0.057 × √(Q × V / RT60) directly — V in m³, RT60 in s, Dc in metres — so the Q for free space, wall, edge or corner is the only judgement call left.

The calculation is based on the specific conditions of your room and the source's placement, with Q=1 for free space, Q=2 for against a wall, Q=4 for an edge, and Q=8 for a corner. The formula accurately models this transition point, providing a vital metric for sound system design and room acoustics optimization. This helps ensure that listeners receive sound primarily from the direct path, avoiding muddiness caused by excessive reverberation.

How to Use This Calculator

Follow these simple steps to calculate the critical distance:

Type the room volume in m³.
Type the measured or predicted RT60 reverberation time in seconds.
Choose the source placement from the dropdown — free space Q = 1, wall Q = 2, edge Q = 4, corner Q = 8.
Read the critical distance Dc in metres, and check the substituted formula line beneath it for verification.

FAQ

Q: What is the critical distance formula for a room?: A: Dc = 0.057 × √(Q × V / RT60), with V in m³, RT60 in seconds, Q the source directivity factor, and Dc returned in metres.
Q: Which Q value do I use for a corner-mounted source?: A: Q = 8 for a corner, Q = 4 on an edge, Q = 2 against a wall, and Q = 1 for free space.
Q: What happens if I enter an RT60 of zero?: A: The tool rejects any RT60 of zero or below and shows an error — RT60 is a divisor in Dc = 0.057 × √(Q × V / RT60), so the value is undefined.
Q: Does doubling the room volume double the critical distance?: A: No — V sits under the square root, so doubling the volume multiplies Dc by √2, about 1.41.