Wave field synthesis needs loudspeakers spaced at most half a wavelength apart.

Evidence

Theoretically, the WFS is superior as a technique, because the perceived position of the sound source is correct within a very large listening area. Unfortunately, to create the desired wave field in the total area inside the array requires that the loudspeakers are at a distance of at most half a wavelength from each other. Arrays for wave field synthesis have been built for room acoustics control and enhancement to be used in theatres and multi-purpose auditoria (Vries and Boone, 1999). — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1907