Variables that influence sound pressures generated in the ear canal by an audiometric earphone.

Abstract

The influence of outer-ear configuration on the acoustic stimulus delivered by a supra-aural earphone to a listener's tympanic membrane was investigated. A probe-tube microphone measured sound pressures generated in the ear canal by a TDH-49 earphone with constant electrical input. Acoustic and anatomical measurements obtained from the ears of Caucasian adults and children (male and female) were analyzed statistically. Mean sound levels measured in the ears of the adult male group were found to be lower than those obtained from the other three groups of ears at all eight test frequencies. Significant differences between groups were found at three of these frequencies. Variation between individuals was partly explained at specific frequencies by certain structural parameters of the ear. Implications of these results are discussed with respect to definition of international auditory standards, design of an improved artificial ear, accurate determination of the threshold of hearing sensitivity, comparisons of hearing between groups, and audiometric evaluation of patients with structurally abnormal ears.