
Engineers create synthetic, sound-silencing structure that blocks 94% of sounds - fezz
https://www.eurekalert.org/pub_releases/2019-03/bu-brd030619.php
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hlieberman
Reading the underlying paper (Ghaffarivardavagh, R., Nikolajczyk, J.,
Anderson, S., & Zhang, X. (2019). Ultra-open acoustic metamaterial silencer
based on Fano-like interference. Physical Review B, 99(2)), this works on a
particular frequency that you can design one of their mufflers for. A 10Hz
change to either side of the target drops the effectiveness from 95%+ down to
below 50%.

Still very cool, and extremely useful for sources like turbines and HVAC
systems that are primarily one or two frequencies, but it's hardly a cone of
silence; it won't block out your co-workers anytime soon.

~~~
tensor
I suppose you could stack several of these on a duct, each designed for a
different range, to get more coverage?

~~~
ChuckMcM
Exactly right, just like stacking filters in a signal path.

With a 10Hz 3dB point, the bandwidth is 20Hz. Your typical engine exhaust has
an acoustic spectrum bandwidth of about 150Hz so a stack of 15 of these would
allow you to overlap your filters by 5Hz on either side and notch the entire
spectrum out. Depending on how much back pressure it put into the system that
could pretty effectively quiet a generator or a turbine.

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downrightmike
This paper came out last year and was on HN
[https://www.researchgate.net/publication/327274462_A_Review_...](https://www.researchgate.net/publication/327274462_A_Review_of_Tunable_Acoustic_Metamaterials)

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tsumnia
More of an aside, but I really like the article they linked [1] because in
addition to scientific explanation, it included a lesson plan and questions
for practice. With the spark in "Nifty Assignments" in CS journals, this was a
nice feature to include.

[1]
[https://www.lencore.com/Portals/5/Lencore_Docs/Article_Under...](https://www.lencore.com/Portals/5/Lencore_Docs/Article_UnderstandingAcoustics.pdf)

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revel
Does this mean we're going to get silencers for leaf blowers? If so, how many
nobel prizes can they be nominated for?

~~~
AstralStorm
No, leaf blowers are way too wide spectrum for this to work. Most of the noise
in them is air moving throw narrow ducts at high velocity.

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tmikaeld
Last time this was posted, I pointed out that it does not block low
frequencies, aka. Bass.

Only high mass can do that, the waves pass straight through everything else.

~~~
amluto
I see no reason at all that a low-mass engineered structure, meta or
otherwise, couldn’t absorb or reflect bass. Silly example: two sheets, with
vacuum in between, held apart by an active structure that transmits constant
force independently of displacement. This will reflect bass. It may not be
_practical_ , but that’s a separate issue.

~~~
tmikaeld
You'd basically need a vacuum box to contain it and wait until the waves
(eventually) run out of energy.

~~~
AstralStorm
Why vacuum if you want to absorb maximum energy? You want liquid or gel
instead.

By the way we have these, they're called bass traps.

~~~
tmikaeld
Sound doesn't travel in a vacuum.

Bass traps work by eating up the energy in pressure waves that hit them,
there's a lot of waves that don't hit them.

Which means that bass traps are only good for minimizing resonances inside an
enclosed room, not to stop bass from reproducing through walls or materials.

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rootsudo
Now that is cool. I can see it being implemented in HVAC/Central Air.

I don't understand how it'd be implemented, in say, an open office?

~~~
Frost1x
Presume you can just tile these in a 2D grid or plane to make a wall you can
see and let air flow through but sound is severely canceled. You'd have to
cover the ceilings as well to avoid reflectance into other open spaces I'm
assuming.

As neat as this is, there are a lot of cases where sound is advantageous for
us humans regardless of when it being annoying, it often can pass useful
information buried in all the rest of the unuseful noise. This is already a
problem in some cars where you can't tell if emergency vehicles are
nearby/incoming or hear other drivers horn signals. Sometimes you want to
ignore this but sometimes it's quite useful.

~~~
standyro
This article neglects to mention that scientists and architects in Silicon
Valley have recently discovered an amazing new technology to improve
productivity for workers in open office plans. It involves creating four
directly connected acoustically designed walls made out of acoustic foam and
eco friendly recycled wood with a fifth addition of a wall above the cubicle,
with a removable door. Interior designers have coined a new term for this
luxury: "private offices"

~~~
erentz
Don't forget that Silicon Valley and aspiring Silicon Valley companies in
order to "be hip" and look like they rented the cheapest warehouse-esque
startup space they could find, require all ceiling tiles be removed to ensure
maximum possible sound reflection in their open plan offices.

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sinab
I'm surprised no one has discussed the possibility of using this device for
reducing snoring sound transmission. I need to read the paper [1] more
carefully but on first glance it seems like the effectiveness is best around
450 Hz and snoring is about 150Hz [2].

[1]
[https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.02...](https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.024302)

[2]
[https://www.ncbi.nlm.nih.gov/pubmed/12071989](https://www.ncbi.nlm.nih.gov/pubmed/12071989)

~~~
AstralStorm
Snoring is too wideband either, and is impulse noise where this is even less
effective.

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wizardforhire
From the image I’d hardly call that a metamaterial. It’s just a novel shape
for a Helmholtz-resonator which if the name didn’t give it away has been known
about for a very long time. I will give them credit for stream lining the
design process.

[https://en.wikipedia.org/wiki/Helmholtz_resonance](https://en.wikipedia.org/wiki/Helmholtz_resonance)

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seltzered_
Wonder if this could be applied for use on computers, partly for reducing
noise on home machines but interesting if there would be any benefit in noise
reduction in datacenters. Or at least an add-on it specialized rack case to
quiet down hardware lab environments.

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proc0
We need over-ear headphones with this ASAP. Current noise dampening products
are mostly targeted for high dB sounds. It would be nice to have pure silence
anywhere with relatively small headphones.

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alltakendamned
While this research is more limited than the title makes it sound, I would
very much be first in line if there ever was a technological breakthrough that
could really block all sound, without requiring one to completely isolate
themselves.

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njaremko
Original discussion:
[https://news.ycombinator.com/item?id=19344682](https://news.ycombinator.com/item?id=19344682)

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RickJWagner
Truly awesome. I hope we get a practical application soon, I'd like to sound-
proof a room for musical instrument practice.

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ohiovr
Could it be used to quiet a submarine turbine?

~~~
AstralStorm
Yes, but not in the useful sense of making the submarine harder to detect with
passive sonar, as most of the vibration is transferred directly into water via
the transmission. The other modes are better dampened with the usual
absorption.

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colsandurz
94% loss is only 12.2 dB (10 * log10(1-0.94) == 12.2)... not that much.

Also, where's the STL if I want to try this myself??

~~~
corporatehobo
Here it is
[https://www.thingiverse.com/thing:3575092](https://www.thingiverse.com/thing:3575092)
I'm going to try it myself.

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dharma1
Not broadband sound, right?

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michaelt
Scientists: We've designed a muffler that can reduce 95% of the noise from a
single-frequency point source aimed down a plastic pipe. Might be useful for
fan noise in ducts.

Journalists: Acoustic metamaterial blocks _all sound_. Soundproof yet
transparent walls. Cubicles will never be the same.

~~~
dang
Ok, we've changed from [https://www.fastcompany.com/90316833/scientists-have-
discove...](https://www.fastcompany.com/90316833/scientists-have-discovered-a-
shape-that-blocks-all-sound-even-your-co-workers) to the press release it
points to and quotes from. Interesting how a press release is more sober and
neutral than a third-party media article.

~~~
gus_massa
Can you also replace the title with the subtitle?

"Boston University mechanical engineers create synthetic, sound-silencing
structure that blocks 94 percent of sounds"

94% seams to be a lot, but it is far from "canceling" the sound. It's only a
-20dB reduction that transform a very loud sound to a loud sound, not to an
inaudible sound.

(Also, it is only useful for a narrow interval of frequencies.)

~~~
dang
Sure, done now.

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Havoc
Soooo....better suppressors for the CIA then?

~~~
BubRoss
Suppressors work by cooling down the exhaust gasses before they reach the air
so that they don't create a burst of expansion.

