Virtual acoustic source
According Huygens principle each point of a wave front starting point of an elementary wave. Therefore would possible synthesize arbitrary wave front completely from such elementary waves. For a sufficient number of such elementary waves, the synthesized wave front hardly differs from the natural wave front. Their starting point establish virtual acoustic source, posing the same characteristics as a natural acoustic source at this position. Their lokalisation no longer dependent from listener position, like the position of a phantom acoustic source during the conventional loudspeaker reproduction. Its direction will perceived everywhere at her virtual starting point. One simple possibility for establishing a virtual acoustic source would be assembling of a lot of single loudspeakers on a spherical surface. It's easily understandable; we perceive the origin of the radiated wave front always in the center of the sphere.
At limited listener range is possible establishing the wave front according Huygens principle electronically by means of loudspeaker array. The radiation of each single loudspeaker delay until the virtual wave front of the virtual sound source would hit the concerning loudspeaker:
If the loudspeakers align in a plane, the acoustic curtain solution becomes possible. Such solution was the dream of the scientists in the 30th of last century already. But the realisation was estimate impossible for all times due to the number channels:
The acoustic curtain idea: One Microphone provides the signal for each assigned speaker on the opposite side of the wall. Like acoustic curtain the loudspeaker wall restore the genuine wave front.
But if we consider more exactly, we don't really need a separate channel for each speaker. The signal doesn't differ in substance, but rather in time. That's a simple task for digital signal processors at present. Besides of the formidable efficiency of such loudspeaker alignment because of the perfect air resistance adaptation of the resulting huge membrane, a lot of new possibilities occur. The directed radiation avoid feeding the mirror sources of the playback room unwanted by energy. By that reason the playback room acoustics losing of influence. Moreover becomes possible by using aimed the playback room wall reflections for fake room sizes and different reflective behavior. As far as the playback room becomes including into the sound field synthesis a largely complete physically restoration of the genuine sound field, comparable the Holography approach in the optical range within reach. The principle is shown by the wave field synthesis site .
next chapter: wave field synthesis