Effect of ear canal wall resonance on measured ear absorbance: A theoretical modeling approach

Wideband tympanometry (WBT) is a promising alternative to conventional diagnostic methods for middle ear disorders. It measures the absorbance (Abs) of sound energy in the middle ear across a wide frequency range, offering the potential for more accurate diagnosis. However, its current clinical application lacks a clearly defined diagnostic basis. This study aimed to clarify the diagnostic basis of WBT by analyzing the relationship between the impedance of each part of the ear and the measurement results through numerical simulations based on the theoretical equations of the middle ear. A major challenge encountered was the significant discrepancy between the simulated and measured values in the high frequency range. To address this, we conducted measurements using tubes simulating the ear canal. This allowed us to investigate the underlying reasons for the characteristic features observed at the high-frequencies and incorporate additional terms into the theoretical equations, thereby resolving the issue. As a result, we found that the theoretical formula requires a term related to radial resonance of the ear canal wall. Furthermore, in some cases, it is also necessary to include increased damping at higher frequencies.