Experimental studies on the assessment of attenuation characteristics and comfort levels of a variety of ear plugs and ear muffs have also been carried out by NIOH. The attenuation characteristics of two models of ear plugs (A and B) and five models of ear muffs (A, B, C, D & E) were assessed in the acoustic chamber. The results showed that both models of ear plugs yielded low attenuation values of 9-11 dB at frequencies 2000-8000 Hz. The ear muff (Model E) afforded maximum sound attenuation (35-40dB) at frequencies 3000-8000Hz. The attenuation values of other ear muffs were relatively low ranging 28-32 dB for model ‘A’, 26-30 dB for model ‘B’, 32-35 dB for model ‘C’ and 15-20 dB for model ‘D’.
Absolute impression of comfortable-uncomfortable sensation (psycho-physical method) produced by the wearing of ear protectors revealed a high percentage of comfort responses for ear muff model ‘E’ due to its overall low application force and especially smaller application force of its headband spring compared to those of the other ear muffs. Models ‘A’ and ‘B’ was graded as less comfortable compared to model ‘E’ because the applied force of these two models was comparatively high as where the tightness of the headbands. Model ‘C’ was rated as less comfortable and model ‘D’ as least comfortable, despite the low application force and less tightness of the spring. Thus the five models of earmuff were graded for comfort in wear.