Changes in the ear canal dimensions with time amongst wearers of custom-molded earplugs

Custom-molded earplugs can be highly effective hearing protection devices because of their personalized fit, which ensures a secure seal. Therefore, the evolution of ear morphology is a crucial factor in the control and monitoring of these earplugs. The first part of this paper describes a large-scale study of the evolution through time of external ear morphology and, especially, the ear canal evolution. Extracted from a database composed of 2 × 106 scans, 411 000 pairs of ear scans were compared, each pair capturing the morphology of a single ear at different times from 1 to 120 months. The whole process has been automated and allows the exhibition of general tendencies of the evolution of the ear canal through time (dilation/contraction). The second part of this paper focuses on the impact of such evolution of the ear canal on the performance of custom earplugs on 24 participants. As the ear canal of the participants cannot be dilated, a dilation of a canal is simulated with a contraction of the earplug that can be observed through age. The attenuation is then measured with a method based on Real Ear Attenuation at Threshold. These two studies show that (i) ear canals tend to dilate over time and (ii) hearing protection may be still effective even after 10 years.