Differences between binaural sound-field thresholds and monaural audiometric thresholds

Abstract

Pure-tone audiograms under earphones and noise-band open-ear sound-field thresholds were collected from more than 150 subjects during hearing protector testing. The pure-tone audiograms were administered with 5-dB resolution to normal-hearing subjects (≤25 dB HTL) with an audiometer using TDH-50 headphones in standard cushions. Sound-field thresholds were determined by presenting a third-octave band noise in a reverberant room for the same subjects at resolution of 1 dB [Franks et al., Ear Hear. 13, 2–10 (1992)]. The subject’s best pure-tone threshold for either ear at each frequency was converted to dB SPL for comparison to the sound-field thresholds. The transfer function between pure-tone, minimum audible pressure, to diffuse sound-field, minimum audible field, was calculated for each of the test frequencies 125–8000 Hz, including 3150 and 6300 Hz. A second experiment was performed with ten subjects where each received three pure-tone audiograms at 1-dB resolution, as well as three sound-field noise-band audiograms at 1-dB resolution. The ten-subject data set was used to test the robustness of the larger data set. The results may be useful for predicting the open-ear sound-field thresholds from a subject’s pure-tone audiogram and in establishing guidelines about test precision of sound-field audiometry.