Divergence of wfs- sources inside the spectator range regarding the associated screen projection

According to the principle of the wave field synthesis virtual acoustic sources approximated in behaviour upon the material acoustic sources on that point. The rendition of audio events was improved by this procedure so clearly, because these virtual sources able to be located much more stably than the phantom acoustic sources, which are produced during conventional rendition with single loudspeakers. Their position does not move any longer also, if the listener in the monitor room moves.

If the loudspeaker arrangement is developed around the listener, the virtual sources may generated at any point beyond or inside the loudspeaker arrangement. In order to hold the expenditure within justifiable borders for practical reasons this arrangement is reduced onto a horizontal loudspeaker line around the listener, without the ability to represent the elevation of the acoustic source. Virtual acoustic sources beyond such loudspeaker arrangement get produced very authentically in this level, however for the reproduction within the rendition arrangement two elementary problems arise:

On the one hand inside the range between the producing loudspeakers and the virtual source overlie the producer field with the user field. Furthermore the concave wave fronts within that range leads to misguiding detections of the source direction, because run time errors between the ears of the listener (ITD) develops. The acoustic waves apparently run into the false direction. Thus the listener may not have a high-quality rendition in that range between virtual source and the loudspeaker arrangement. These artefacts may reduced with well-known procedures so far, not eliminated however until now.

Besides the optical impression agrees for only one listener place with the acoustic impression for virtual acoustic sources within the spectator range during a coupled image representation. That is to be clarified on the basis the representation in Fig.1:

It shows a loudspeaker line (1a) according to the principle of the wave field synthesis, arranged ring around the listeners. The listeners within the spectator range (1b) see the plotted acoustic source (1d) on the screen (1c). For the listener position (1e) within the spectator range the featured virtual acoustic source (1f) can be produced for a reference, on which the sound impression formidable agrees with the image representation. For all other listeners within the spectator range differs the optical impression and the acoustic perception for such virtual acoustic source, represented within the listener range.

The listener some rows in front (1g) hears the signal source represented before itself on the screen from the rear. In addition the concave wave fronts and the overlay lead the false detections at its place to, so that this range between the screen and virtual source is not usable. For the spectator (1h) the acoustic source is in front right visible, he hears it however exactly beside itself. The direction difference is acceptable for the spectator (1i), it hears however the acoustic source much too quietly. Also for him the acoustic perception does not agree with the optical one, which makes the whole perception completely improbable.

The consequence is, that with the wave field synthesis in practice no virtual source, which is assigned to the position of an acoustic source within the spectator range in a simultaneous image representation, can be generated, if the demonstration of several recipients is to be pursued at the same time. Therefore the possibility of the wave field synthesis procedure, to reproduce acoustic sources close at the listener, may be used only very restricted. But this occur as one of the most significant advantages of the wave field synthesis, because the close representation of acoustic sources for the Reception is one of the most important emotional factors.

The acoustic perception of the virtual source within the spectator range does not differ in principle from the acoustic perception of a material acoustic source at this point. Though the problem results from the fact, that the optically noticed signal source in the parallel image representation can not be produced also at this space point. That fact will not be changed in the future by three-dimensional projection too. But the problem is solvable in large extend. Solution is described on the DE 10 2006 054 961 A1 application.

It describes the way for maintaining the perceived source position still, if the physically source position become shifted onto a noncritical location. Thats possible, if all first reflections become approperiate changes.