Evaluation of a high-order Ambisonics decoder for irregular loudspeaker arrays through reproduced field measurements

High-order Ambisonics (HOA) is a sound field reproduction technique that defines a scalable and system-independent encoding of spatial sound information. Decoding of HOA signals for reproduction using loudspeaker arrays can be a difficult task if the angular spacing between adjacent loudspeakers, as observed from the listening position, is not uniform. In this research, one of such systems is considered: a 157-channel irregular loudspeaker array. The array is used to reproduce simple HOA-encoded sound fields. Three HOA decoding methods are evaluated: two conventional ones and a recently proposed decoder designed for irregular loudspeaker arrays. Reproduction accuracy is compared by directly measuring the sound pressure around the listening position, the so-called sweet spot. Coarse-resolution sound field measurements give an approximate size for the listening region generated by the different methods. In addition, dummy head recordings are used to evaluate interaural level and phase differences. The results are used to estimate the accuracy of the system when presenting spatial sound. This study shows the importance of selecting a proper decoding method to reproduce HOA with irregular loudspeaker arrays. This is emphasized by the use of an actual loudspeakers system instead of a computer simulation, a common shortcoming of previous studies.