Attenuation as a function of the canal length of custom-molded earplugs

Abstract

The fit of a custom-molded earplug (CMEP) and the amount of attenuation it provides can be affected by variables related to the original earmold impression and the subsequent manufacturing process. One variable thought to affect the amount of attenuation is the length of the canal portion of the CMEP. In this pilot study, we systematically examined the relationship between CMEP canal length and attenuation in four human subjects. Two men and two women were fitted with CMEPs extending past the second bend of the ear canal. The attenuation provided by the CMEPs was measured over four visits to the laboratory. Prior to each visit, the canal portion of the subject's test CMEP was shortened by 2mm. As expected, attenuation decreased as canal length decreased for all subjects. However, the rate and pattern of decrease varied markedly. Anecdotal reports of comfort as a function of canal length also varied markedly. Results suggest that the critical region/s in the ear canal for maintaining a good acoustic seal may vary from person to person. Implications for future study will be discussed. © 2013 Acoustical Society of America.