Wave field synthesis

Wave field synthesis (WFS) is a spatial audio rendering technique, characterized by creation of virtual acoustic environments. It produces artificial wavefronts synthesized by a large number of individually driven loudspeakers from elementary waves. Such wavefronts seem to originate from a virtual starting point, the virtual sound source. Contrary to traditional phantom sound sources, the localization of WFS established virtual sound sources does not depend on the listener's position. Like as a genuine sound source the virtual source remains at fixed starting point. WFS is based on the Huygens–Fresnel principle, which states that any wavefront can be regarded as a superposition of spherical elementary waves. Therefore, any wavefront can be synthesized from such elementary waves. In practice, a computer controls a large array of individual loudspeakers and actuates each one exactly by the time and level, at which the desired virtual wavefront would pass through its point. By that way fom a mono signal source a genuine wave front of a sound source may by restored. The basic procedure was developed in 1988 by Professor A.J. Berkhout at the Delft University of Technology. Its mathematical basis is the Kirchhoff–Helmholtz integral. It states that the sound pressure is completely determined within a volume free of sources, if sound pressure and velocity are determined in all points on its surface. Therefore, any sound field can be reconstructed, if sound pressure and acoustic velocity are restored on all points of the surface of its volume. This approach is the underlying principle of holophony. For reproduction, the entire surface of the volume would have to be covered with closely spaced loudspeakers, each individually driven with its own signal. Moreover, the listening area would have to be anechoic, in order to avoid sound reflections that would violate source-free volume assumption. In practice, this is hardly feasible.