Cross-talk in otoacoustic emission probes.

Objective: Several commercial otoacoustic emission probes (Virtual 330, Etymotic Research ER-10 and ER-10B, and Otodynamics ILO88 and ILO92) were tested for internal coupling (cross-talk) between the sound source and probe microphone.
Design: The response of the probe under test was measured, in a cavity that simulates the human ear canal, first in its normal configuration and then with either the sound source tube or the microphone inlet blocked with modelling clay. Cross-talk was indicated if the pressure failed to drop substantially in the "blocked" condition.
Results: Cross-talk in the Virtual 330 and Etymotic ER-10B was found to be severe enough to compromise the accuracy of "in the ear" acoustic calibrations. In both cases the cause was the radiation of sound through the walls of the flexible silicone tubing used to conduct the stimuli through the body of the probe. Substituting harder-walled sound source tubing reduced cross-talk to levels acceptable for routine application. The probes used in the otodynamics ILO88 and ILO92 systems and the original Etymotic ER-10 probes all have acceptably low cross-talk as supplied from the manufacturers.
Conclusions: For the two probes where excessive cross-talk was found, most of the cross-talk was acoustic and/or mechanical, rather than electromagnetic. Artifacts due to cross-talk have undoubtedly contaminated data collected with these units. Manufacturers of emission probes are urged to adopt a standard for specifying cross-talk levels and include this specification in product literature.