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Received Sep 19, 2017; Revised Nov 24, 2017; Accepted Nov 28, 2017
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction
Soldiers and supporting engineers are commonly exposed to high cabin noise in military vehicles, which includes firing noise and/or cabin booming noise. The energy content in such noises generally falls in the low-frequency range (<500 Hz). Typically, automobile manufacturers apply several passive and/or active acoustical treatments for cabin noise control. However, the maximum acoustical performance of the treatments may not be achieved due to other design considerations [1]. In practice, the simplest approach is to highlight the importance of hearing protection to the soldiers and engineers on the correct procedures in wearing hearing protection devices, earplugs and earmuffs (or ear defenders).
Earplugs are generally preferred as they are easy to put on and do not cause as much discomfort as earmuffs. Furthermore, they are inexpensive and, in a way, dispensable. However, poor fitting of earplugs is still a problem observed among some employees [2, 3], consequently compromising noise attenuation. In a study by Toivonen et al. [2], they reported a drop in noise attenuation of up to 10 dB when the earplugs were poorly fitted into the ear canals. However, the drop might not be necessarily due to the lack of user knowledge but could also be due to incompatible ear canals. Nonetheless, earplugs are usually inadequate in typical military environments. As such, earmuffs are typically recommended. One key advantage is the nondependency of acoustical performance on one’s ear canals. If properly worn, earmuffs can provide better noise attenuation than earplugs [4]. Commercially, a wide selection of earmuffs is available, catering...