Schroederdiffusor

A Schroederdiffusor, commonly called a Schroeder diffuser or quadratic residue diffuser (QRD), is an acoustic device designed to scatter sound reflections and create a diffuse sound field. It is used to reduce strong reflections, flutter echoes, and spatial irregularities in rooms, contributing to clearer and more even listening environments.

The diffuser consists of a row (or a two-dimensional array in larger installations) of wells or cavities with varying depths. The depths are chosen according to a quadratic residue sequence (modulo the number of wells), producing a pseudo-random distribution of reflection phases across the panel. When sound waves strike the surface, the differing path lengths to the bottom of each well impart different phase delays, spreading reflected energy in many directions and improving spatial diffusion.

In practice, QRD panels are typically constructed from wood or composite materials and mounted on walls or ceilings. They are most effective in the mid to high frequency range, where the well depths correspond to practical dimensions. For very low frequencies, the required depths become large, so QRD diffusers are often used in combination with other bass treatment methods rather than as stand-alone solutions.

Schroeder diffusers are available in various sizes and configurations, from small studio panels to larger architectural installations. They are favored for their predictable diffusion characteristics, relatively simple construction, and compatibility with other acoustic treatments. Related diffuser concepts include all-pass and two-dimensional diffusion arrays, which extend the same principle to broader spatial coverage.