Attenuation of dual hearing protection: Measurements and finite-element modeling

In extremely noisy environments, it is normally recommended to use a combination of earplug and earmuff, denoted here as a dual protection, to protect workers from the excessive noise. Unfortunately, it has been shown repeatedly that the attenuation values obtained with the dual protection are generally less than the sum of the individual earplug and earmuff attenuation values. In the literature, this is generally explained by the bone conduction path and the coupling between the earplug and the earmuff. However, there is much less work devoted to examining in detail the coupling between the earplug and the earmuff. In this work, experimental results on human subjects and on an artificial text fixture are collected using REAT and MIRE procedures for different combinations of earmuffs and earplugs. Additionally, a finite-element model is used to investigate the physics of the problem and to better understand the nature of the coupling between the earplug and the earmuff when used in a dual configuration. Results from the experimental procedures as well as from the FE model are presented and discussed. These results clearly illustrate the importance of the coupling between the earplug and the earmuff when used in combination.