Acoustic-reflex dynamics and the loudness-discomfort level.

Acoustic-reflex growth functions and Loudness-Discomfort Level (LDL) measures were obtained for 15 normal-hearing subjects. The hypothesis that signals considered uncomfortably loud occur at intensity levels that produce proportionately equal acoustic-reflex magnitudes was evaluated. Individual reflex growth functions were measured as a function of activator SPL for a 1000-Hz tone, a 4000-Hz tone, and a broadband noise. These growth functions were measured within subjects (two trials) and across subjects in terms of (a) percentage acoustic-impedance change at LDL, (b) percentage acoustic-reactance change at LDL, (c) acoustic impedance at LDL, (d) relative change in acoustic impedance at LDL, and (e) ratio of static acoustic impedance to change in acoustic impedance at LDL. Although the loudness and acoustic-reflex measures demonstrated good reliability across trials, the data showed large variability across subjects and did not support the experimental hypothesis. It was concluded, therefore, that the use of acoustic-reflex measures in the estimation of an individual's LDL is unwarranted.