Yup- potato masher are acoustic lenses too. Only real point I was trying to make is "non-directional" might describe the vanes better than "directional". The idea was to create a softer edge wide pattern rather than the narrow one from a horn alone. They do alter the sound, and so have somewhat fallen out of favor. But everything old eventually becomes new again. Line arrays caused diffraction horns to make a comeback. BTW WE had acoustic lenses back in the '30's.

Interesting illustration of a circa 1960 Westrex system....
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For serious geeks only:

Computer Simulation of Pressure Fields Generated by Acoustic Lens Beamformers

acoustic

Bang & Olufsen are bragging about their "new" acoustic lens technology....