Mathematical shape that blocks sound

Researchers at Boston University recently conducted an experiment where a loudspeaker was placed at one end of a PVC pipe, cranked up and out came nothing. What…nothing how is that possible? The other end of the PVC pipe was left open except for a small 3D-printed ring placed around the rim. The ring was able to cut 94% of the sound coming from the speaker making it inaudible to the human ear. Called an acoustic meta-material the ring was printed from a mathematical design, that is shaped in such a way that it can catch certain frequencies passing through the air and reflect them back toward the source. Read the full article.