Fresnelcut

Diffuser

2D Quadratic-Residue Diffuser

A 2-D QRD replaces the row of slots with a grid of square wells, so it scatters sound both horizontally and vertically. It is the right choice when reflections arrive from more than one plane — for example on a ceiling cloud or a large rear wall.

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How it works

The depth of the well at grid position (i, j) is set by `(i² + j²) mod N` over an N×N grid of prime N. Because it scatters in two axes, one module already breaks up reflections well; tiling several modules across a wall benefits from modulation to avoid a repeating lattice — Fresnelcut turns that on automatically.

Each cell is a square block of a set footprint. The deepest cell drives how thick your stock needs to be, which Fresnelcut reports as you design.

The math
d(i,j) = [(i² + j²) mod N] · λ₀ / (2N)

An N×N grid (prime N). The additive residue array is what gives two-axis scatter.

Best for

  • Ceiling clouds and large rear walls
  • Rooms where reflections come from several directions

Not the tool for

  • Bass problems (use an absorber)
  • Tight side-wall strips where 1-D scatter is enough

Start from a common size

N is the number of wells (a prime). More wells scatter more smoothly but make a wider, deeper panel. Pick one to open the designer pre-set:

Related reading

Related panel types

See all diffuser & absorber types.