Modelling Speech Intelligibility in the Noisy Work- place for Normal-hearing and Hearing-impaired Listeners Using Hearing Protectors

Abstract

A speech intelligibility model was developed and validated for use in workplace environments with hazardous noise levels that require the use of hearing protection devices (HPDs). Two speech perception studies were carried out in laboratory simulations of eight workplace noise environments. The first experiment (n = 32 normal-hearing individuals) was used to develop a general model for speech intelligibility that can be tuned to the specific characteristics of the noise. The second experiment (n = 35) was used to validate the general model for use with listeners covering a wide range of hearing profiles (up to severe hearing loss) and wearing HPDs (earplugs or earmuffs). The model took into account the characteristics of the noise, the signal-to-noise ratio (SNR), the attenuation of the hearing protector, and the hearing status of the listener. Good prediction of speech intelligibility scores in noise with HPDs required the use of correction factors to deal with both audibility (threshold) and distortion (supra threshold) effects arising from hearing loss. Correction factors due to audibility effects were computed from the Speech Intelligibility Index and the pure-tone audiogram. Correction factors due to distortion effects were based on the Hearing-in-Noise Test.