Effects of earplug hearing protectors on the intelligibility of Persian words in noisy environments

Purpose: Noise is one of the most important problems in the workplace. The main adverse effect of exposure to this physical pollutant is the hearing loss. For preventing such adverse effects, the use of hearing protective equipment is recommended. Despite the simplicity, hearing protective equipment can affect the correct perception of the words in a conversation. Methods: 32 students of Iran University of Medical Sciences with normal hearing were randomly selected and the speech intelligibility test (Speech Discrimination Test (SDS), using Ampaid plus, A177 audiometer) was performed on them. Each participant took the speech intelligibility test under four different conditions: without noise or earplugs, with noise but without earplugs, with noise and 25 Noise Reduction Rating (NRR) earplugs, with noise and 32 NRR earplugs. In each stage, the speech intelligibility test was repeated for each individual at signal-to-noise (S/N) ratios of +10, 0, and �10 (N = 85 dB, S = 75, 85, 95 dB). Results: The results demonstrated that maximum speech perception (89.75) occurred without noise or earplugs, while minimum speech perception (8.13) occurred with noise and without earplugs at S/N = �10. Results also revealed that hearing protectors (25 or 32 NNR earplugs) improve the average value of intelligibility. This value is greater with 25 NRR than with 32 NRR earplugs. Conclusion: Based on the results obtained, we can say that in the presence of background noise, hearing protectors increase the speech intelligibility; and the lower the NRR, the higher the intelligibility. Because of the inconsistent results of the studies in this field, and since speech interference and miscommunication in the workplace can lead to irreparable damage, more comprehensive research is required. © 2018 Elsevier Lt