On the design of an acoustical test fixture for assessing the objective occlusion effect

Abstract

Earplugs are widely used to prevent noise induced hearing loss. However, the discomforts they induce negatively impact their effectiveness by influencing their consistent and correct use. The occlusion effect discomfort is related to an increased perception of the bone-conducted part of physiological sounds (e.g., one’s own voice, breathing and chewing) when one’s earcanal is occluded. The discomfort experienced could be objectively estimated by calculating the objective occlusion effect, which is the difference between the tympanic sound pressure levels in the occluded and open earcanals when exposed to the same stimulation of a bone transducer. To avoid direct measurements on human participants, this work proposes an acoustical test fixture (ATF) for quantifying the objective occlusion effect. The proposed ATF employs an anatomically realistic truncated ear, incorporating soft tissues, cartilage, and bone components to replicate the outer ear bone conduction path crucial for occlusion effect assessments. It is shown that the proposed ATF can reproduce key effects observed in objective OE measurements on human participants: (i) significant OE at low frequencies, diminishing with increasing frequency, (ii) reduction of OE with greater insertion depths, and (iii) distinctions among various earplug types, particularly noticeable at deeper insertions compared to shallow ones. The proposed ATF can therefore be used to design in-ear devices with a reduced occlusion effect, leading to an improved experience for many users of hearing protectors, hearing aids, and earbuds. Additionally, a computationally efficient Finite Element Method-based virtual tester for the ATF is developed and validated. This virtual tester is employed to deepen the comprehension of the physical phenomena that underlie the observed vibroacoustic behavior of the proposed ATF. It also opens avenues for future research aimed at re-evaluating ATF design parameters and enhancing OE assessment.