Magnitude spectra for a 4 Hz infrasound, measured with the low-noise ER-10B+ microphone, in the ear canal of four listeners (green solid lines) and the corresponding spectra in the B&K 4157 occluded-ear simulator (black solid lines). Each panel shows the result of one listener. In all panels, the spectra are limited to the frequency range from 2 Hz to 38 Hz. The reference thresholds are shown as a black dashed line, the individual thresholds as red crosses. Black arrows indicate ear-generated distortion products, which were identified by means of criteria described in the text (see also Fig. 5).