Effect of wearing hearing protectors on the audibility of warning signals for normal and hearing-impaired listeners: experiment and model

International audienceThe audibility of warning signals is of paramount importance in noisy industrial environments to ensure the workers? safety. In practice, several factors may compromise the audibility of warning signals, such as the presence of background noise, the use of hearing protector devices (HPDs) and the hearing impairments of the workers. First, in order to evaluate the effect of HPDs on the audibility of railway warning signals, masked thresholds were first measured in the laboratory in the presence of 86(A) low-frequency background noises, both with and without wearing the HPDs. Seven warning signals and two HPDs (custom molded earplugs and a passive earmuff) were tested on normal-hearing (NH, N=18) and hearing- impaired (HI, N=62) subjects with various hearing loss profiles. The results show that for NH subjects, the audibility is generally improved when wearing the HPDs (i.e. the protected thresholds are lower than the unprotected thresholds). For HI subjects, the audibility may be impeded when wearing the HPDs (i.e. the protected thresholds are higher than the unprotected thresholds) and the impediment tends to increase with increasing hearing loss. Second, using these experimental data, a model was developed to predict masked thresholds. This model is based on the Signal Detection Theory (SDT) and the Glasberg and Moore excitation pattern model (Glasberg BR, Moore BCJ. Derivation of auditory filter shapes from notched-noise data. Hearing Research. 1990;47(1-2):103-138). The excitation pattern model was modified to take into account both enlarged auditory filters and elevated absolute thresholds of HI listeners. Using this model, the experimental trends were fairly well reproduced. However, some improvements could still be made to better the precision of the predictions