On the influence of the middle ear on the sound pressure level generated in open and occluded earcanals under a bone-conducted stimulation

The occlusion effect is an acoustic discomfort commonly encountered by earplugs’ users, which corresponds to the increased auditory perception of the bone-conducted sound mainly at low frequencies. This perception is accompanied by the augmentation of the sound pressure level in the earcanal when occluded by the earplug compared to the open case. While the source of the SPL generated in the earcanal in both open and occluded cases is mainly attributed to the vibration of the earcanal wall, the sound radiation of the tympanic membrane that stems from the middle ear vibration is commonly considered as not significant. To investigate this phenomenon, a finite element model that incorporates the middle ear components into a realistic human outer ear is developed. First, the finite element model is evaluated by comparing the acoustic impedance computed at the eardrum surface to literature data obtained on human subjects. Second, the finite element model is used to quantify the contribution of the sound radiation that originates from the middle ear on the sound pressure level generated in both open and occluded earcanals under a bone-conducted stimulation.