Distortion product emissions arise only in a live ear, not passive cavities

Evidence

Figure 3.25 shows an example for the distortion product at the frequency (2JI - h) = 2 x 1620 Hz - 1851 Hz = 1389 Hz and its cancellation. Two primaries are shown in the lower trace with the probe placed in a passive cavity instead of in the outer ear canal. It is thus shown that no measureable distortion product appeared at 1389 Hz, where the noise floor is more than 85 dB below the 1620-Hz primary. Placing the probe in the outer ear canal of a normally hearing subject, a distortion product emission at 1389 Hz is clearly indicated in the upper trace. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 334

Categorization

• XREF: Confirms the emission is physiologically generated in the cochlea, not an acoustic artifact — ties to cochlear amplifier / otoacoustic emission research.