Nonspherical Microphone Arrays for Mixed-Order Ambisonics: Optimized Design and Performance Analysis

Sound field recording aims to capture and preserve the sound field in the area of interest. One of the well-known sound field recording techniques, higher-order Ambisonics, utilizes spherical harmonic decomposition to conduct the recording. Furthermore, to improve the performance near the horizontal plane, mixed-order Ambisonics (MOA) has been proposed. However, the typical spherical microphone arrays used in higher-order Ambisonics are not well-suited for MOA, and existing microphone array design methods for MOA are empirically based. To address these limitations, this paper proposes an optimized design method for microphone arrays specifically used in MOA. The authors begin by formulating the MOA encoding process as an objective function to minimize. Analytical gradients with respect to microphone positions and baffle shape parameters are derived to facilitate efficient gradient-based optimization. Based on these derivations, a unified framework that simultaneously optimizes both microphone positions and baffle shape is introduced. Numerical simulations validate the effectiveness of the proposed method, demonstrating that the optimized arrays result in lower MOA encoding errors and superior robustness compared to conventional designs.