Application of a circular 2D hard-sphere microphone array for higher-order Ambisonics auralization

A circular microphone array mounted on a rigid sphere was realized and its application to higherorder Ambisonics (HOA) auralization was analysed. Besides the 2D Ambisonics application this array design provides a promising basis for the development of a mixed-order Ambisonics recording system, in which the high spatial resolution of a high-order 2D system is efficiently combined with a periphonic sound field representation of a low-order 3D system.

In order to evaluate and optimize the performance of the spherical 2D microphone array, a versatile simulation framework was developed, which included the entire processing path from the sound source via the (noisy) microphone signals and the loudspeaker output signals to the reproduced sound field in the centre of a loudspeaker array.

This framework was then used to analyse the response of the different system stages to an ideal plane wave. The simulation results showed very good agreement with corresponding plane wave recordings in an anechoic chamber and thus, confirming the general applicability of the simulation framework. An overall preference listening test was performed to estimate the optimal array radius and amount of regularization, two (dependent) parameters that mainly determine the balance between low frequency directionality, signal coloration and microphone noise amplification.

The different stimuli were created with the framework using different values for both the array radius and the regularization coefficient lambda. It was shown that best results were achieved with a radius of around 5-10 cm and a lambda of about 0.01.