QRD diffuser calculator & guide

A quadratic residue diffuser (QRD) scatters sound evenly using a row of wells with carefully chosen depths.

How a QRD works

Each well's depth follows the sequence n² mod N, where N is a prime number. Sound reflecting from wells of different depths returns with different delays, so the reflection spreads out instead of bouncing back like from a flat wall.

Choosing the settings

• Prime N — the number of wells in one period. Larger primes give more, finer wells.
• Design frequency — the lowest frequency the diffuser is tuned for. Lower frequencies need deeper wells.
• Well width — narrower wells keep diffusion working to higher frequencies.
• Max well depth — limits the panel thickness for your room and printer.

1D and 2D QRD

A 1D QRD has long slots and spreads sound in one direction. A 2D QRD uses a grid of square wells and spreads sound in both directions — it's the same idea as a skyline diffuser.

Design one online

Diffuser Designer calculates well depths for you, shows the diffusion graph live as you change settings, and exports 3D-printable STL files — split to fit your printer if needed.