Far field onset distances vary widely by source size and wavelength

Evidence

Beranek (1986) suggests that the far field begins at a distance of three to ten times the largest dimension of the sound source. At this distance the source is small compared to the distance, and a second criterion is normally satisfied: distance2 = wavelength2/36. Evidently, there is academic ambiguity about where far field begins. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1267

Categorization

• DEFINE: Defines the engineering rule of thumb for where far-field conditions (and thus valid anechoic measurements) begin.