Acoustic Metamaterials Can Block 94% of Sounds

Synthetic, sound-silencing structures—acoustic metamaterials can block 94% of sounds. This ring of materials will be able to make vacuum cleaners, air conditioners, fans and other devices and products much quieter.

Boston University researchers Ghaffarivardavagh and Zhang wanted to block sound but not open air.

They calculated the dimensions and specifications that the metamaterial would need to have in order to interfere with the transmitted sound waves, preventing sound—but not air—from being radiated through the open structure. The basic premise is that the metamaterial needs to be shaped in such a way that it sends incoming sounds back to where they came.

They modeled the physical dimensions that would most effectively silence noises. Bringing those models to life, they used 3D printing to materialize an open, noise-canceling structure made of plastic.

Trying it out in the lab, the researchers sealed the loudspeaker into one end of a PVC pipe. On the other end, the tailor-made acoustic metamaterial was fastened into the opening.

Standing in the room, based on your sense of hearing alone, you’d never know that the loudspeaker was blasting an irritatingly high-pitched note. Inside the PVC pipe, you would see the loudspeaker’s subwoofers moving.

The team found that they could silence 94 percent of the noise which making the sounds emanating from the loudspeaker imperceptible to the human ear.

Physical Review B- Ultra-open acoustic metamaterial silencer based on Fano-like interference


Recently, with advances in acoustic metamaterial science, the possibility of sound attenuation using subwavelength structures, while maintaining permeability to air, has been demonstrated. However, the ongoing challenge addressed herein is the fact that among such air-permeable structures to date, the open area represents only small fraction of the overall area of the material. In the presented paper in order to address this challenge, we first demonstrate that a transversely placed bilayer medium with large degrees of contrast in the layers’ acoustic properties exhibits an asymmetric transmission, similar to the Fano-like interference phenomenon. Next, we utilize this design methodology and propose a deep-subwavelength acoustic metasurface unit cell comprising nearly 60% open area for air passage, while serving as a high-performance selective sound silencer. Finally, the proposed unit-cell performance is validated experimentally, demonstrating a reduction in the transmitted acoustic energy of up to 94%. This ultra-open metamaterial design, leveraging a Fano-like interference, enables high-performance sound silencing in a design featuring a large degree of open area, which may find utility in applications in which highly efficient, air-permeable sound silencers are required, such as smart sound barriers, fan or engine noise reduction, among others.

SOURCES- Boston University, Physical Review B

Written By Brian Wang

24 thoughts on “Acoustic Metamaterials Can Block 94% of Sounds”

  1. You can silence muzzle blast reasonably well, but a supersonic bullet makes a loud crack…can’t be silenced.

  2. Have you made and used a silencer?

    Maybe leave the judgement about their actual function to people who have.

  3. The noise of a ducted lift fan is, to a great extent, the high velocity air stream hitting the rest of the atmosphere.

    You can’t build a barrier around the entire volume of air beneath the aircraft.

    Well, I suppose you COULD.

  4. About a year ago, I saw a motorcyclist enter a grocery parking lot just going slowly. Didn’t think much of it until he found an old lady with her back turned struggling with her groceries then he got right behind her and revved the snot out of his hog and left the parking lot. She managed to hold onto the groceries despite the 130 decibels. Absolutely right…@$$holes. The only reason he was in the parking lot was to terrorize old ladies.

  5. It always amazes me that anyone could think legions of poorly educated people running around with machine guns and silencers is a beneficial condition to any society. Modern societies have an interest in keeping implements of mass butchery with low societal benefits out of the reaches of such individuals. Everyone is theoretically law abiding up until the moment they choose not to be, some capabilities should never just be a matter of individual choice.

    Anyone who thinks existing silencers are “simple and effective” have been watching too many movies.

  6. Nah, it could work for scooters but not for motorcycles. Even now, nobody would buy a quieter bike. There’s no showoff…

  7. Except in the US, where they’ve been legally treated like machine guns. Because, if you can’t take somebody’s guns away, at least you can hope for them to go deaf.

  8. 94% of the noise is a trivial level of reduction, because of the logarithmic response of human senses. I’m assuming what was meant was a 94% reduction in decibels?

  9. Yes, the dust problem is the issue for the first application I thought of, a car exhause muffler.

  10. There are already materials that can make closed spaces quiet. This thing allows air movement while dampening sound. Should be great for computer cases, room fans, and car AC systems. One I’d really like to see is air impact wrenches, and other air tools, like nailguns, and air grinders. These tools are very cheap, powerful and light, but they tend to be inefficient (the compression of the air initially and the inefficiencies of the air motor) and very very loud.

    You could even have an entrance to a loud nightclub with a tunnel walkway through this. Almost quiet at one end, but as you walk through it gets louder and louder.

    Definitely like to see this compulsory on motorcycles.

  11. What’s the odds they made it in the shape of an earring. What’s that. Couldn’t hear you.

  12. I wonder if it would work equally on white noise. A monotone is not a useful test for a general application. Another real issue is probably particle contamination. Metamaterials are fine structured. Dust and particles will disable the device.

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