Objects must span a radian of phase shift before meaningfully interacting with sound.

Evidence

Sometimes it is also useful to use a quantity called the wavenumber that describes how much the phase of the wave changes in a given distance. Again, it is a form of “ruler” that is in units of radians per meter (rad m−1); most physical objects need to have a phase shift of at least a radian across their physical size before they will really interact with a sound wave. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 150

Categorization

• XREF: Connects to the reader’s interest in how physical objects interact with acoustic waves — links to architectural acoustics and how obstacles scatter or pass sound.