Effects of mandibular motion on earplug function

Abstract

Earplug attenuation depends on developing and maintaining an acoustic seal between the earplug and the walls of the ear canal. During use, earplugs may lose some of their effectiveness by loosening over time and with activity, thereby compromising the acoustic seal in the ear canal and allowing more sound to enter the ear canal from the sound field. Mandibular motion (as during talking, singing, chewing, breathing) provides a nearly continuous source of ear canal movement resulting from forces applied by the condyle of the mandible. Individual differences in ear canal geometry also may impact the effects of mandibular motion on earplug function. The effects of mandibular motion on earplug function were investigated using an acoustic test fixture that combined (1) individualized pinna and ear canal structure beyond the second bend, inclusive of the mandibular bump, with (2) a standardized ear simulator (GRAS RA0045) with ear canal extension and microphone (GRAS 40AH ¼”). Mandibular motion was simulated using a computer-controlled drive-pin with a silicone tip that articulated with the mandibular bump of the individualized silicon ear canal. Results indicated that as few as 50 cycles of mandibular motion could significantly compromise earplug function and that this compromise was highly subject-dependent.