Improvement of Occupational Noise‐induced Temporary Threshold Shift by Active Noise Control Earmuff and Bone Conduction Microphone

Improvement of Occupational Noise‐ induced Temporary Threshold Shift by Active Noise Control Earmuff and Bone Conduction Microphone: Seichi Horie. Department of Health Policy and Management, Institute of Industrial Ecological Science, University of Occupational and Environmental Health—A newly devised earmuff that utilizes an active noise control system and a bone‐ conduction microphone was examined in an actual working environment where workers are required to communicate under noisy conditions. Thirteen experienced male workers aged 26 to 46 (mean ± SD; 37.5 ± 5.8) engaged in manufacturing steel pipes participated in the study. For 4 h working in a noisy environment (92 to 103 dBA), they used the conventional device (an earphone on one ear and an earplug in the other, and an ordinary microphone) or the new device. After wearing the new device, the temporary threshold shift (TTS) at 4 kHz was lowered (p<0.045, Wilcoxon's sign rank test) and the number of workers who had TTS was reduced in all frequencies examined (p<0.001, two‐way repeated‐measures ANOVA). Many workers evaluated the new device superior to the conventional one especially in its “clearness of voice,” but they did not give the new device a good overall rating mainly because of its heaviness. Although the new device needs improvement, it appears promising as a hearing protector.