Study of noise reduction rate of the hearing protection devices based on microphone in real ear (MIRE) under laboratory conditions

Nominal noise reduction rate of the earmuff manufacturers can be different compared with the actual attenuation rate. The present study aimed to determine the actual noise reduction rate of current hearing protection devices using a microphone in real ear method.
In this study, five common ear muffs used in the Irans industries was investigated on 30 subjects under laboratory conditions. Noise reduction rates of ear muffs were measured based on the ISO 11904 standard, microphone in real ear method, using noise dosimeter (SVANTEK, model SV 102) equipped with a microphone SV 25 model which can install inside the ear. The ear muffs comfort was also assessed by the developed questionnaire.
The results showed that the real noise reduction rates of the ear muffs are between 49% to 86% nominal reduction rates. Moreover, the actual attenuations are much lower than the nominal reductions at low noise frequencies. The performances of ear muffs developed by Irainian and foreign manufacturers were not statisticaly different (pv> 0.05). Based on subjects comfort scores, comfort of ear muffs were within the acceptable range. The noise reduction rates of the different ear muffs of each model were not also statisticaly different (pv > 0.05).
Since the duration use of earmuff is important factor on the effective protection of hearing, irregular use of the ear muff can reduce real attenuation of the earmuff lower than the minimum rate acquired in this study. Proper training and adequate supervision on the proper use of the ear muff can affect earmuff fitting along with increasing of actual noise attenuation.