Relationship between attenuation characteristics of hearing protectors and speech intelligibility in noise

Masahiro HASHIMOTO1

Abstract: In industrial workplaces, it is widely believed that the use of hearing protectors interferes with speech communication and with the perception of warning signals. The objective of this study was to evaluate the effect of the attenuation of hearing protectors on speech perception in noise. In the experiment, the intelligibility of Japanese sentences presented at two speech levels (65 and 85 dBA) in pink noise was assessed for ten normal-hearing adults, using three protectors with different attenuation characteristics. The noise level was altered at signal-to-noise ratios (SNR) of 0, +5, and +10 dB. The results showed that speech intelligibility was significantly influenced by type of protector, speech level, and SNR. The interaction between these factors was statistically significant. In general, the wearing of the earplug with decreased low-frequency attenuation did not help to improve the intelligibility of speech presented in noise. Correlations between the average attenuation for a specific frequency range and the speech intelligibility were poor, indicating that the attenuation characteristics of the protectors have little effect on speech intelligibility in noise. These results imply that a reduction in the attenuation should not be considered as a countermeasure against the problems of speech communication with hearing protectors.