Vertically separated drivers comb-filter around the crossover, right where hearing is most sensitive

Multi-driver nearfields split the spectrum with a crossover, but around each crossover frequency two physically separated drivers both radiate. If their distances to the ear differ, the signals arrive out of phase and comb-filter. On affordable two-way monitors the crossover sits in the 2–3 kHz midrange, so the comb filtering lands where hearing is most sensitive, subtly corrupting tone and level judgments for vocals, snares, and guitars. Vertical head movement makes the effect most audible.

Examples

Play pink noise through one two-way speaker on-axis, then drift six inches vertically: the tonal change is far larger than the same horizontal move, exposing driver comb filtering.

Assessment

Explain why a two-way monitor comb-filters worst in the midrange and why vertical listening-position changes reveal it more than horizontal ones.