Film-Tech Forum ARCHIVE: a shape that blocks all sound

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Posted by Frank Cox (Member # 6258) on 03-12-2019, 10:31 PM:

Scientists have discovered a shape that blocks all sound

quote:
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.

Now if I can only get a pair of earmuffs to tune out the sound of my own chewing, they’ll really have something.

youtube demo

Posted by Harold Hallikainen (Member # 5405) on 03-12-2019, 10:46 PM:

This sounds like a perforated screen! http://www.acousticdirections.com/wp-content/uploads/smpte_mot._imag._j-2012-long-46-62.pdf#page=11 figure 28. At 5 kHz, about half the power is reflected back from a perforated screen (reflection is 3 dB below forward power).

Harold

Posted by Bill Brandenstein (Member # 7758) on 03-13-2019, 04:29 PM:

The audio in the YouTube video shows a drop of 13.5dB, or about 79%. Granted, that's no scientific measurement, but even the claimed 94% is a reduction of about 24dB, not the total elimination of the sound. That doesn't negate how exciting and useful this invention will be, but it will hardly silence a drone, to be sure, even if you could actually contain all of its noise in a pipe.

Posted by Frank Cox (Member # 6258) on 03-13-2019, 04:37 PM:

I can see where it would be useful in HVAC applications.

Posted by Marcel Birgelen (Member # 6801) on 03-13-2019, 04:40 PM:

Although the idea sounds intriguing, it doesn't look like this is a technology which can easily be adapted as a general sound-proofing solution.

The article is very light on the details, I've got the feeling this only works for a very limited frequency range and that the ring needs to be adjusted to work with other ranges.

Also, I doubt it will have any noticeable impact on deep basses. The only thing that really seems to help against those is still a lot of mass to dampen them.