A minority of listeners show quadratic distortion that depends non-ideally on level and phase.

Evidence

Most of the subjects show the behaviour described above. However, a smaller group shows a dependence of the cancellation level on the level of the primaries that cannot be approximated by the dashed lines. Additionally, for these subjects, the phase is no longer independent of level. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1543