What is the highest SPL that you should use if you're trying to record valid OAEs?
Because the OAE is a byproduct of the operation of the cochlear amplifier, you should use a stimulus that is of low to moderate intensity, one that will evoke a response from the amplifier mechanism. If the stimulus exceeds the level at which the amplifier saturates, then, paradoxically, the response may be insensitive to the status of the cochlea.
Gorga, Neely and Dorn (2002) illustrate that DPOAE saturation is also related to the frequency region of the primary stimuli, becoming apparent when the level of F1 (the lower frequency primary tone) exceeds 65-70 dB for primary tones in the region of 500, 4000 and 8000 Hz.
Another way to answer the question is to determine how well the DPOAE screen performs in terms of identifying individuals with hearing loss. Stover et al (1996) cited by Gorga, Neely and Dorn (2002) demonstrated that optimal performance occurs when the primary tone levels are in the vicinity of 55-60 dB for F1 and 45-50 dB for F2 (that is to say, L1 is 10 dB below L2).
Finally, if one is using high intensity primary tones (e.g., greater than 70 dB SPL) to record DPOAE and encounters a very small DP in the presence of the high intensity primary tones, it would be prudent to rule out the presence of distortion caused by the instrumentation. The DPOAE from a healthy periphery is approximately 60 dB below the primary tone levels. If you encounter distortion just above the noise floor, at a level 80 to 90 dB below the high intensity primary tone, recheck results in a passive system such as a plastic coupler.
Ref: Gorga, M., Neely, S.T., and Dorn, P.A. (2002) Distortion product otoacoustic emissions in relation to hearing loss. In Otoacoustic Emissions (2nd edition) edited by M. Robinette and T. Glattke. pp 243-272 Theime.
Theodore J. Glattke, Ph.D., Professor Speech and Hearing Sciences, University of Arizona, Tucson, AZ