Introduction:One of the recommended methods for evaluation effectiveness of hearing protection is use the acoustic fixture accordance with standard ISO 4869-3. The aim of this study was evaluate the acoustic performance of fixture for using in noise reduction rate  tests of hearing protection devices in the laboratory.

Methods: In this cross-sectional study , noise reduction rates of  five common ear muffs used in the Iran industries were investigated based on the ISO 11904 standard, microphone in real ear method, using noise dosimeter (SVANTEK , Model SV102) equipped with microphone SV25 model which can install inside the ear on 30 subjects under laboratory conditions. Also, noise reduction rate of earmuffs was determined using the fixture model AVASINA9402 accordance with standard procedures.  Data were analyzed using the software SPSS21.

Results: The results showed the real noise reduction rates of the earmuffs on the studied subjects are from 59% to 94% nominal reduction rates. That rates for the ear muffs on the studied fixture are from 64% to 92.The results showed that the noise reduction rates of the ear muffs on subjects compared with and noise reduction rates of the ear muffs on fixture were not statistically significant (p> 0.05).

Conclusion: The results showed the accuracy of noise reduction rate of earmuffs using the fixture compared with real subjects is acceptable. Hence, the fixture is good choice for environments where there’s no possibility of acoustic evaluation on real subjects, also for quality control of productions in the earmuff manufacturers.