Diffusive surfaces scatter sound only within a bounded frequency band.

Evidence

At the lowest design frequency for these examples, a well of depth 5 would correspond to λ 2 . At higher frequencies, the sequences still have the same properties and thus scatter sound effectively. However, when the frequency gets high enough so that λ 2 becomes equal to the minimum difference in depths (1), then the surface again becomes equivalent to a flat surface. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2094

Categorization

• DEFINE: Clarifies that a quadratic-residue surface loses diffusion once half-wavelength shrinks to the smallest depth step.
• QUESTION: Worth checking how much high-frequency scattering matters perceptually versus specular reflection.