Influence of the number of loudspeakers on the timbre in horizontal Ambisonics reproduction

Ambisonics is a series of flexible spatial sound systems based on spatial harmonics decomposition of sound field. It is able to reconstruct sound field accurately within some region and below some frequency limit which are imposed by Shannon-Nyquist spatial sampling theorem and determined by the order of Ambisonics. Above the Shannon-Nyquist limit of spatial sampling, errors occur in the reconstructed sound field, resulting audible artifacts. By using Moore's revised loudness model, the present work analyzes the influence of number of loudspeakers on timbre in horizontal Ambisonics reproduction. The binaural loudness level spectra (BLLS) of Ambisonics reproduction are calculated and then compared with those of target sound field. The results indicate that below the Shannon-Nyquist limit of spatial sampling, the BLLS for Ambisonics reproduction match well with those of target sound field and thus no timbre change occurs. Above the limit, however, the BLLS for Ambisonics reproduction deviate from those of target sound field. The extent of deviation depends on both the direction of target sound field and the number of loudspeakers. Increasing the number of loudspeakers in Ambisonics reproduction may increase the change of BLLS in some case, but may reduce the change of BLLS in some other case.