The relationship between sound transfer functions from free sound field to the eardrum and temporary threshold shift

Three groups of 12 subjects were utilized for an experiment in which the temporary threshold shift due to a free-field exposure was measured and compared to the sound transfer functions from free-sound field to the subjects' eardrums. Subject selection was based upon their sound transfer functions and the requirement of normal hearing. The subjects were assigned to one of three groups depending on their dominantly sound transfer function frequency: Low, middle, or high. A probe tube with a miniature microphone was used for the measurement of the sound transfer functions in 1/3-oct bands. The measurements were performed in frequency bands from 0.2 to 20 kHz with one direction of sound incidence: 0 degree azimuth and 0 degree elevation. The subjects were exposed twice to a 2-kHz and twice to a 4-kHz narrow-band noise monotonically on four different occasions. Pre- and postexposure sweep Békésy audiograms were recorded and the temporary threshold shift calculated as the difference between the two. The averaged temporary threshold shifts differed significantly among groups.