Inverted and delayed sound sources cancel at low frequencies but reinforce higher up

Evidence

For example, for the case of two sources, if there is both delay and inversion, then, at very low frequencies, the sources will tend to cancel each other out, because the effect of the delay will be small. However, as we go up in frequency, the sources will add constructively when the delay causes the sources to be in-phase; this will be at a lower frequency than would be the case if the sources were not inverted with respect to each other. — David Howard, Jamie Angus, coustics and Psychoacoustics, 232