Focusing of virtual sound sources in higher order Ambisonics

Higher order Ambisonics (HOA) is an approach to the physical (re-)synthesis of a given wave field. It is based on the orthogonal expansion of the involved wave fields formulated for interior problems. This implies that HOA is per se only capable of recreating the wave field generated by events outside the listening area. When a virtual source is put inside the loudspeaker array, strong artifacts arise in certain listening positions. These artifacts can be significantly reduced when a wave field with a focus point is reproduced instead of a virtual source. However, the reproduced wave field only coincides with the desired one in one half-space defined by the location and nominal orientation of the focus point. The wave field in the other half-space converges towards the focus point.