Here’s a three-fer of recent acoustics news:
From Physics World, a story about a structure that can block certain sound frequencies. But even cooler, the researchers can change their mind about which frequencies get blocked, and change the material in less than a second: Acoustic metamaterial can be reconfigured in a jiffy.
Meanwhile, from Scientific American, the acoustic equivalent of an optical isolator makes it possible for sound to go from point A to point B, but not back from B to A. This might seem simple, but it hasn’t been done before. A One-Way Street for Sound.
And finally, courtesy of the American Physical Society, we get a story about another metamaterial — foam — which can also block certain frequencies. Although I suspect this was already known to many a garage band, who were asked to muffle their sound by putting rigid foam insulation against the walls. Still, the researchers made a thorough scientific study of what works and how. And probably not playing covers of the greatest hits of Nirvana. Physics – Stopping Sound with Foam.