Acoustic transmission through the human middle ear from infrasonic to audible frequencies: a computational biomechanics study

The human middle ear acts as a frequency-dependent acoustic transmission system coupling sound pressure to inner-ear fluid motion. While its behavior has been extensively studied in the audible range, its response to infrasonic stimulation remains poorly characterized. Here, three middle-ear configurations were simulated using finite-volume modeling: a simplified structural model, a fluid–structure interaction model including a cochlear fluid domain, and an anatomically realistic model reconstructed from micro–computed-tomography data. Harmonic pressure excitations (4–4000 Hz; 70–120 dB sound-pressure levels) were applied to the tympanic membrane, and stapes displacement was quantified at the oval window. Across all models, a linear relationship between sound intensity and stapes displacement was observed. Similar amplitudes were obtained with and without cochlear fluid loading, indicating limited inertial coupling. Resonance-like behavior emerged in the mid-audible range and was consistent with published numerical predictions. Parametric analysis identified tympanic-membrane diameter and thickness, together with annular-ligament morphology, as the main determinants of amplitude variability, whereas footplate and oval-window geometry had negligible influence. These findings demonstrate that middle-ear acoustic transmission remains linear and continuous from infrasonic to low-audible frequencies, supporting simplified boundary conditions in acoustic and cochlear models involving low-frequency sound exposure.