A team of Boston University researchers recently stuck a loudspeaker into one end of a PVC pipe. They cranked it up loud. What did they hear? Nothing.
How was this possible? Did they block the other end of the pipe with noise canceling foams or a chunk of concrete? No, nothing of the sort. The pipe was actually left open save for a small, 3D-printed ring placed around the rim. That ring cut 94% of the sound blasting from the speaker, enough to make it inaudible to the human ear.
The mathematically designed, 3D-printed acoustic metamaterial is shaped in such a way that it sends incoming sounds back to where they came from. [Photo: Cydney Scott/Boston University]
Dubbed an “acoustic meta-material,” the ring was printed from a mathematically modeled design, shaped in such a way that it can catch certain frequencies passing through the air and reflect them back toward their source. Typical acoustic paneling works differently, absorbing sound and turning the vibrations into heat. But what’s particularly trippy is that this muffler is completely open. Air and light can travel through it–just sound cannot.
The implications for architecture and interior design are remarkable, because these metamaterials could be applied to the built environment in many different ways. For instance, they could be stacked to build soundproof yet transparent walls. Cubicles will never be the same.
The researchers also believe that HVAC systems could be fitted with these silencers, and drones could have their turbines muted with such rings. Even in MRI machines, which can be harrowingly loud for patients trapped in a small space, could be quieted. There’s really no limit to the possibilities, but it does sound like these silencers will need to be tailored to circumstance. “The idea is that we can now mathematically design an object that can blocks the sounds of anything,” says Boston University professor Xin Zhang, in a press release.
