Comparison of focusing by time-reversal techniques and WFS

Time-reversal acoustic focusing and focused sources reproduced by Wave Field Synthesis (WFS) are closely related in the underlying physical concepts. However, the goal of time-reversal techniques is typically to concentrate acoustic energy at the focus point, whereas WFS aims at creating an acoustic impression. I have created two videos for my talk at the 127th Convention of the Audio Engineering Society in order to show the difference of the approaches.

The first video shows the reproduction of a focused source using a time-reversal technique on a very densely spaced loudspeaker array (illustrated by the black line). The speakers emit a bandlimited Dirac pulse with a bandwidth of 5 kHz.

Note, the video does not start at the time the pulses have been emitted by the loudspeakers.
The second video shows the reproduction of a focused source using Wave Field Synthesis

Note that the target listening zone is below the focus point.

Its clearly oberservable that the time-reversal technique creates two wavefronts that pass a listener, while WFS creates only the desired wave front within the target zone.

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