As wavelength shrinks below diaphragm size, speakers beam and off-axis sound diverges spectrally

Evidence

However, at higher frequencies, shorter wavelengths, the radiated sound will become more focused in the forward direction of the diaphragm, radiating in a progressively narrowing, and possibly irregular, beam with increasing frequency. This is illustrated in a very simplified manner in Figure 9.17(a); when the wavelengths approach and eventually become smaller than the diaphragm of the loudspeaker, it becomes more directional. This is a problem because the off-axis, room reflected, sound cannot have the same spectral balance as the direct sound. This affects sound quality and spatial effects. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1009

Categorization

• XREF: Connects to the cone-and-dome loudspeaker design tradeoffs and to psychoacoustic work on how off-axis vs direct sound energy affects perceived timbre and spatial impression.