It is well-known that sound is a wave, in the same way that light can be described as one. Waves, no matter if they are mechanical or electromagnetic, share properties. Any wave can be diffracted and therefore focussed in one physical point.
Known to most of us are lenses which focus light, they are used in cameras, telescopes and magnifying glasses. Less intuitive is the fact that this principle can be applied to sound. The particular shape of the acoustic lens causes sound to diffract in such a way that there is one perceivable focus a few meters away from the lens in which the volume is maximal. If one moves a few centimeters away from this point, the volume decreases drastically. An interactive sound landscape is created.