Behold, the tube of silence, er, significantly reduced sound

March 13, 2019 4:14 PM

The science reporting hype promises a bit too much ("Scientists have discovered a shape that blocks all sound–even your co-workers," per Fast Company article title), but the demonstration video of the Acoustic Metamaterial Noise Cancellation Device is pretty impressive, demonstrating "acoustic metamaterial and noise cancellation device capable of blocking up to 94% percent of the transmitted sound energy while preserving air flow." From Dr. Xin Zhang's Laboratory for Microsystems Technology at Boston University.

The paper (paywalled): Ultra-open acoustic metamaterial silencer based on Fano-like interference (published on Physical Review B, via Research Gate)

Also, ENG’s Xin Zhang Is BU’s 2018 Innovator of the Year, First Woman Chosen

Xin Zhang is well-known for her pioneering work with metamaterials in areas as diverse as magnetic resonance imaging (MRI), downwell sensor technology for the oil industry, and noise-cancellation acoustics. A College of Engineering professor of mechanical engineering, she is the director of BU’s Laboratory for Microsystems Technology (LMST), which focuses on interdisciplinary research in microelectromechanical and nanoelectromechanical systems.

posted by filthy light thief (24 comments total)

is there a shape that blocks people's faces?
posted by Foci for Analysis at 4:19 PM on March 13, 2019 [10 favorites]

Yes, it's called a hand. Or a book. Or a newspaper. Or a wall. ;)

But the beauty of this is that it's an open shape, which lets light and air pass through, but significantly cuts the sound.
posted by filthy light thief at 4:25 PM on March 13, 2019 [1 favorite]

The science reporting hype promises a bit too much
Isn't that considered a scientific constant these days?
posted by oneswellfoop at 4:33 PM on March 13, 2019 [1 favorite]

Any citation in a standard unit like dB? A percentage could mean a few different things when talking about difference in sound level.
posted by idiopath at 4:34 PM on March 13, 2019 [3 favorites]

So it's a muffler? Hmm, ok....
posted by sjswitzer at 4:34 PM on March 13, 2019

...but significantly cuts the sound.

For values of 'significantly' meaning 12 dB (so 'standing by an air-raid siren' becomes a soothing 'standing next to a speaker stack at a rock concert').

It also only operates at a single frequency.

It's openness is a neat variant on the many acoustic metamaterials that have been produced in the last decade or so, but it's of primarily theoretical interest at this point. While there may be a handful of applications that have these very precise requirements, many, many more improvements and extensions would have to happen before this would have any widespread practical utility.
posted by BlueDuke at 4:38 PM on March 13, 2019 [10 favorites]

(I'm saying 12 dB based on one comment I found which claims a reduction in the 'sound energy' by 94%. If it's really a reduction in the sound amplitude, then it would be a 24 dB reduction)
posted by BlueDuke at 4:40 PM on March 13, 2019 [1 favorite]

So does this mean that the noise the upstairs neighbors make could be reflected back on them?
posted by Bee'sWing at 4:43 PM on March 13, 2019 [3 favorites]

science reporting hype promises a bit too much

Yeah my co-workers all make pure sine waves at the same frequency.
posted by tclark at 5:17 PM on March 13, 2019 [21 favorites]

Get back to me when it comes in cone form.
posted by sysinfo at 5:45 PM on March 13, 2019 [9 favorites]

But then you won't be able to hear us.
posted by Greg_Ace at 6:02 PM on March 13, 2019 [5 favorites]

Gesticulate at me when it comes in cone form.
posted by sysinfo at 6:27 PM on March 13, 2019 [18 favorites]

Yeah my co-workers all make pure sine waves at the same frequency.

Just wait until the new guy shows up and then your office background oooooooooooooooooooooooo becomes oOo.oOo.oOo.oOo.oOo.oOo.
posted by a snickering nuthatch at 7:04 PM on March 13, 2019 [13 favorites]

This seems promising for reducing noise in research or commercial settings where airflow may be important to the working of the machine (you can't just block off an exhaust pipe). While not sine tones, I can imagine several of these in a row to cut the fundamental frequency and the loudest harmonics. If it's relatively cheap to produce, I could see it becoming widespread; if not, it might still have applications in research where a very quiet environment is desirable.

Interesting, and a good post.
posted by solarion at 8:07 PM on March 13, 2019 [1 favorite]

Dyson makes a lot of money on those bladeless fans, but they are quite loud, running at a fixed speed and so generating noise at a fixed (more or less) frequency. Perhaps this is something that could be used to make a much quieter bladeless fan.
posted by davejay at 10:41 PM on March 13, 2019

Moving air only makes noise when it encounters something moving at a different speed from itself and turbulent flow ensues. If wind were noisy in and of itself, those fluffy outdoor shotgun microphone covers would not be able to improve the signal to noise ratio of recordings made in windy conditions to anything like the extent that they do.
posted by flabdablet at 2:21 AM on March 14, 2019

Even if this could quiet your coworkers, management would convince themselves that loud, distracting, open-plan offices are essential for "collaboration", and would refuse to install it.
posted by escape from the potato planet at 4:13 AM on March 14, 2019 [4 favorites]

Can we paint it vanta black?
posted by srboisvert at 6:04 AM on March 14, 2019 [6 favorites]

> So it's a muffler? Hmm, ok....

That was my thought too. The claim is that it preserves airflow, but the disk's diameter is smaller than the pipe it is attached to, so airflow has to be impeded at least a little.

Still, if it's more compact and efficient than a muffler while presenting less resistance to airflow, that's still a big accomplishment.
posted by ardgedee at 7:22 AM on March 14, 2019

I strongly am convinced that if you try to undo the noise made by the movement of air from a fan you are basically undoing the movement of the air from the fan. I could be wrong in this, but it feels gut-level correct.

The air's kinetic energy can be thought of as coming from two phenomena: the flow of air from one place to another, and the vibrating motions about a particular spot. The flow is what we want from a fan. The back-and-forth motions are what produces the sound (when that disturbance reaches our ears).

Now, flows of air can produce vibrations as a side effect. Wind instruments do this. Perhaps surprisingly, these instruments convert just a single-digit percentage of the air's kinetic energy into sound. Most of the energy in a fortissimo brass blast is still just the air flowing out of the instrument, not the air's back-and-forth motion.

This is, of course, even more true of a fan, whose sole purpose is to push (not shake) air.
posted by a snickering nuthatch at 9:04 AM on March 14, 2019

On the other hand, Researchers suggest phonons may have mass and perhaps negative gravity. Which has the horrible implication that maybe that WTF weirding module from that Dune adaptation could be a thing.

Muad'Dib
posted by zengargoyle at 9:54 AM on March 14, 2019 [2 favorites]

That article makes no sense. As stated by others, a 94% reduction in audio power is only 12 dB, which is nothing.
There's a press release linked from the Fast Company article that words it differently:

"By comparing sound levels with and without the metamaterial fastened in place, the team found that they could silence nearly all--94 percent to be exact--of the noise, making the sounds emanating from the loudspeaker imperceptible to the human ear."

Which could mean 94% of the frequency spectrum of the noise is reduced more significantly, essentially silencing those frequencies.

But even that press release is badly written, with gems like this:

"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. If, however, you peered into the PVC pipe, you would see the loudspeaker's subwoofers thrumming away."

Subwoofers thrumming out a high-pitched note?
posted by rocket88 at 10:15 AM on March 14, 2019 [3 favorites]

Subwoofers generate harmonics, just like any other speaker. I imagine the fundamental would have to be very thoroughly dampened for them to be audible though.
posted by ardgedee at 4:49 PM on March 14, 2019

subwoofers are constructed to produce a narrow and low range of frequencies, who knows what was meant because the text is nonsense
posted by idiopath at 3:21 AM on March 15, 2019 [1 favorite]