Comparative study of attenuation measurement of hearing protection devices by real ear attenuation at threshold method

Abstract

Aim: The aim of the present study was to find out the measurement of real protection of ear muffs and as well ear plugs along with comparison of the efficacy of different hearing rotection devices (HPDs) in attenuation of stimulus levels for various stimuli by real ear attenuation at threshold method. Materials and Methods: Subject group consisted of ten males with the mean age of 20 years having normal hearing sensitivity (pure tone audiometry (PTA) less than 25 dB). Sound field measurement of thresholds was carried out for various stimuli, that is, warble tone, narrow band noise, and speech noise. Frequencies from 250 Hz to 12 KHz were tested in a sound treated room. For comparison, experimenter personally fitted the HPDs, that is, ear muff using experimenter fit method. Occluded threshold levels, that is, threshold of audibility for the test signals were measured in exactly same way as was done for open thresholds. The same procedure was followed for ear plugs also. Measurements were summarized at each frequency in terms of grand mean and a standard deviation of the protection values for both HPDs. Results: In all cases the mean attenuation was similar to optimum figures suggested in the literature, but the standard deviation was relatively high. Ear plugs produce more attenuation for low as well as high frequencies of warble tone and narrow band noise, but ear muff are better attenuators at mid frequencies for both warble tone and narrow band noise and also for speech noise stimulus. Conclusion: The attenuations provided by different types of HPDs vary across various nature and frequencies of that noise. This is to be kept in mind while suggesting for appropriate type of Hearing Protection Devices [HPDs] for optimal benefit.