Scattering Coefficient

A measure (0-1) of how much reflected sound energy is scattered versus specularly reflected.

The scattering coefficient (s) quantifies the proportion of reflected sound energy that is scattered (non-specularly reflected) versus mirror-reflected. It ranges from 0 to 1:

• s = 0: Perfect mirror reflection (flat wall) • s = 1: All reflected energy is scattered away from the specular direction • Typical diffusers: s = 0.5 to 0.9

Unlike the diffusion coefficient which describes angular uniformity, the scattering coefficient measures the total amount of energy redirected away from the specular direction. A surface could scatter all energy (s=1) but send most of it in one direction, resulting in high scattering but low diffusion.

The scattering coefficient is measured according to ISO 17497-1, using a random-incidence method in a reverberation room. ISO 17497-2 measures a related but different quantity — the directional diffusion coefficient — using a free-field method; the two answer different questions and aren't interchangeable. Measurements vary with frequency, so results are typically reported in octave or third-octave bands.

For room acoustic modeling, the scattering coefficient is essential for predicting how surfaces will affect the sound field.

Practical Example

Comparing surfaces

Flat drywall: s ≈ 0.05 | Bookshelf: s ≈ 0.3 | QRD diffuser: s ≈ 0.7-0.9

A QRD scatters 70-90% of incident energy away from the mirror angle, while flat drywall reflects almost everything specularly.

Standards: ISO 17497-1

Glossary · Diffuser Designer

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