Modal analysis of asymmetry vocal fold vibration and sound

Asymmetric vibration of the vocal fold is a typical symptom of dysphonia. Understanding the intrinsic relationship between vocal fold vibration patterns and the resulting acoustic signals is beneficial for developing presurgical planning tools for treatment. In this study, the acoustic properties of asymmetric oscillation are investigated by varying the stiffness of the vocal fold. A fluid-structure-acoustic interaction (FASI) model is developed, in which the vocal fold is modeled as a continuous medium, and the fluid-structure interaction is captured via two-way coupling at their interface. Acoustic pressure is computed using the Linearized Perturbed Compressible Equations (LPCE). The modes of solid deformation, the sound source field, and the acoustic field are extracted and analyzed using the Spectral Proper Orthogonal Decomposition (SPOD) method. The predicted amplitude of the acoustic signal ranges from 2 to 4 Pa, approximately 10% of the hydrodynamic pressure amplitude, demonstrating the validity of the present model. For both symmetric and asymmetric vocal fold vibrations, the dominant mode shares the same frequency but exhibits different mode shapes. Symmetric vibration generates both compression and expansion acoustic modes, whereas asymmetric vibration retains the compression mode while suppressing the expansion mode. In this way, asymmetric vocal fold vibration acts as an acoustic rectifier, leading to reduced phonation efficiency. This mechanism will be further analyzed for three-dimensional vocal fold vibration.