Geometrical Acoustics Simulations for Ambisonics Auralization of a Car Sound System at High Frequency

Nowadays, numerical simulations are the key tool for car audio systems and interiors design, since they allow estimating the acoustic response, thus the listening experience. This requires simulating the transfer path between each loudspeaker of the sound system and the listening position, which may be described, for instance, through a spherical harmonic expansion of the sound field; hence, permitting to auralize the sound system through real-time binaural decoding of the Ambisonics format over a head-tracked Head Mounted Display (HMD). In this paper, two numerical methods were compared for calculating the spatial impulse responses in High Order Ambisonics (HOA) format: ray tracing and pyramid tracing, respectively implemented in Comsol Multiphysics and Ramsete. The latter is equipped with a built-in post-processor capable to compute multichannel impulse responses in various formats including Ambisonics up to fifth order. An external post-processing tool was developed to calculate the Ambisonics impulse responses of Comsol Multiphysics simulations. First, the two methods were cross validated with two test cases: free field propagation and a room model. Results were compared in terms of time of arrival (ToA) of the direct sound, reverberation times, octave band spectra and accuracy of the source localization. Afterwards, the sound system of an existing high-end car was simulated. The results were compared with a set of experimental measurements performed inside the cockpit of the real car, employing a spherical microphone array.