AMTAS®: Automated method for testing auditory sensitivity: III. Sensorineural hearing loss and air-bone gaps
Conclusions: From 0.5 to 8.0 kHz, occlusion effects produced by the circumaural earphone are sufficiently small that covering the ear does not appreciably alter bone-conduction thresholds. Air-conduction threshold differences warrant further study to determine if reference equivalent threshold sound pressure levels for the two earphones produce equivalent thresholds. The large air-bone gap at 4 kHz suggests the possibility of an incorrect reference equivalent threshold force level at that frequency.
from the International Journal of Audiology