Diffuser Calculator — QRD Well Depths

QRD Sequence

s(n) = n² mod N (where N is the chosen prime number)

Well Depths

Depth(n) = s(n) × wavelength / (2 × N)

The wavelength is calculated from the design frequency and speed of sound. Each well depth creates a different path length, scattering reflected sound evenly across a wide angle.

Frequency Range

Upper limit = c / (2 × well width) — set by how narrow each well is.

The "design frequency" here is the depth-quantum reference that sets the well-depth steps, not literally the lowest diffused frequency. Useful scattering extends roughly one octave below it (down to about half the design frequency), so the lowest effective figure is reported as f₀/2.

Genuine low-frequency diffusion also needs the panel period width to be at least one wavelength of the lowest frequency you want to scatter. A single short period (for example seven 40 mm wells = 280 mm wide) is only one full wavelength wide at ~1.2 kHz (c/0.28 m ≈ 1225 Hz), so below that the panel is too narrow to diffuse properly — use a double or triple period to actually scatter the lower end of the stated range.