Reflection from rough surfaces smooths detail once wavelengths exceed roughness

Evidence

Diffuse surfaces, on the other hand, scatter sound in other directions than the specular. In the case of an ideal diffuser, the scattered energy polar pattern would be in the form of a hemisphere. A simple approach to calculating the effect of this can be to model the scattered energy as a source whose initial intensity is given by the incident energy. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2318 (#expands, via linked claim)

Categorization

• XREF: connects to: Whether a surface reflects or scatters waves depends on roughness relative to wavelength; Reflection and diffraction of sound both depend on object size relative to wavelength; How bumps reflect sound depends on bump height relative to wavelength. (+3 more)

Broader Connections

• Whether a surface reflects or scatters waves depends on roughness relative to wavelength #expands (0.95)
• How bumps reflect sound depends on bump height relative to wavelength. #exemplifies (0.90)
• Diffuse surfaces scatter sound hemispherically rather than mirror-like #expands (0.85) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2318
• Diffusion depth scales proportionally with wavelength, so lower frequencies demand deeper surfaces #expands (0.80)
• Reflection and diffraction of sound both depend on object size relative to wavelength #qualifies (0.75)