The most common way to reduce noise exposure in the workplace is to wear hearing protection devices (HPDs). The negative effect of wearing HPDs is, however, attenuation of both unwanted noise and wanted signals. This negative aspect of HPDs is amplified by the fact that typical HPDs attenuate high-frequency sounds (speech, warning signals) more than the low frequency sounds (many industrial noises). The common practice of selecting HPDs by providing as much noise attenuation as possible, leads therefore, to overprotecting of the wearer who may not hear high frequency warning signals, sudden changes in machine noise, and other important acoustic signals such as speech. A flat attenuation HPD, i.e., an HPD which noise attenuation is frequency independent, may facilitate speech communication by eliminating overprotection of the HPD user at high frequencies. However, this cannot be achieved by providing less than adequate protection against existing noise levels. Thus, the proposed study is designed to evaluate the relationship between noise attenuation and speech communication effectiveness resulting from wearing flat-attenuation HPDs in several simulated work environments. Various objective and subjective measures will be compared to assess the amount of noise attenuation by the protectors as well as the effectiveness of speech communication between workers wearing the protectors. The following measures will be directly obtained or calculated in the study: real-ear attenuation at threshold, sound pressure level reduction, word recognition score, speech intelligibility rating, double-task performance effectiveness, speech level adjustment, and vocal effort. The results of this study are expected to determine noise spectra and ranges of noise levels which are appropriate environments for wearing flat-attenuation HPDs. Collected data will also be used to assess efficacy of various speech communication measures for assessment of HPDs.
