Abstract
In previous work, the authors have proposed the earplugs that pass a specific frequency of sound, with simple structured analog acoustic band pass filters consisting of a micro-orifice, a flexible elastic plate and a small weight. These earplugs could efficiently let workers in noisy factories to protect their ears and, at the same time, to hear the necessary sounds for communicating with colleagues, noticing danger alarm sounds, and detecting equipment failure noise, etc. In this study, to evaluate the influence by acoustic properties of individual ear, the insulation performance of the suggested filtered earplug are calculated and measured in the cases of using an occluded-ear simulator and a simple straight pipe coupler. The calculation model of the insulation property of the proposed earplug is derived with the transfer matrix method, considering the acoustic transfer impedance of the ear simulator, which is specified in IEC 60318-4 (2010). The results in calculations and experiments are closely matched and that shows the validity of the calculation model. These experimental and calculation results also confirm that the proposed earplug has the function to pass a specific frequency of sound even in actual use. Furthermore, it is considered that the proposed earplug may have the robustness to the differences of the acoustic properties of individual ears.
