Audiometer-Earphone Mounting to Improve Intersubject and Cushion-Fit Reliability

Abstract

The range of combined intersubject and cushion-fit variation in the response of the TDH-39 audiometer earphone in an MX41/AR cushion, reported in the literature and confirmed in these measurements, is of the order of 25 dB at 100 Hz, 6 dB at 1 kHz, and 15 dB at 5 kHz. The performance of this earphone system is further impaired by cushion-induced physiological noise that masks low-frequency thresholds, typically by 6 dB in normal-hearing subjects. An experimental mounting for the TDH-39 is described and analyzed; it is a circumaural device designed to keep the earphone-ear acoustical system as near constant as possible with successive fittings and different subjects, and to reduce physiological noise. The performance of the TDH-39 in this mounting, compared to performance in an MX41/AR cushion, showed a substantial reduction in cushion-fit and intersubject response variation, and masking by physiological noise was largely eliminated in the subjects tested. The mounting has an optional cup for reducing the transmission of external noise, but this reduction is at the expense of a partial return of physiological noise masking. Average midrange sensitivity was reduced 5–6 dB. Response measurements were made with a free-field reference method, using a probe microphone at the subject's eardrum.

Pitch identification of simultaneous dichotic two-tone complexes

“…This noise masked unwanted partials that might arise as aural distortion products (Plomp, 1965;Goldstein, 1967;Humes, 1980). Stimuli were presented diotically, i.e., with both partials going to both ears, through TDH-49 headphones with circumaural oil-filled cushions (Villchur, 1970). Subjects seated in a sound-proofed chamber were instructed to play each note back on a five-note keyboard.…”

Comparison of DT 48, TDH 49, and TDH 39 earphones

“…Between DT 48 and TDH 49 (both without equalizer) /XL equals 5 dB. Thus, moderate differences in real-ear frequency response show up which are due to the different systems and cushions (Shaw, 1966;Villchur, 1970). …”

Physical characteristics of headphones used in psychophysical experiments

“…The sizes of air gaps, which alter actual-ear response a lot, vary a lot depending on a shape and materials of the cushion. Thus, actual-ear response can be improved by contriving the shape and materials of the cushion [17,25,26]. As…”