
An “acoustic metamaterial” that can cancel 94 percent of sound - njaremko
https://www.bu.edu/research/articles/researchers-develop-acoustic-metamaterial-noise-cancellation-device/
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tmikaeld
As far as deep bass goes, this won't hinder that - since bass waves have too
high of a pressure to not pass through the object.

The most effective material is high mass and flexible, like cork or hemp
crete.

Bass-traps also exist, they eat up the energy of sound pressure and are
usually large tubes and many of them are needed to make a difference.

So there's a reason that this test is on high-frequencies, not low ones.

EDIT: Fine, down-vote me if you want but it doesn't make it less true [1]

[1] [https://www.acousticfields.com/how-do-you-stop-low-
frequency...](https://www.acousticfields.com/how-do-you-stop-low-frequency-
issues-in-a-small-room/)

~~~
IshKebab
You might be being downvoted because you've confused frequency with amplitude.
Bass means low frequency / long wavelength. It doesn't say anything about
amplitude / pressure.

~~~
TheOtherHobbes
Bass carries more energy, and the waves have higher pressure as well as a
longer wavelength.

You can attenuate treble with a sheet of toilet paper, but you need a lot of
mass to stop bass of equivalent nominal level.

~~~
hexane360
Your result is correct but your explanation is all kinds of wrong. First,
shorter wavelength waves have higher energy. Second, amplitude doesn't cause
the difference here. Even if you needed 1000W of bass to get the same effect
as 10W of treble, 50% attenuation of bass would sound the same as 50%
attenuation of treble.

The real difference is that waves are attenuated much more by objects larger
than their wavelength.

~~~
TheOtherHobbes
Sound isn't light. If you have source for your suggestion that shorter
wavelengths of sound carry more energy, I'd be curious to see it.

And no, the real difference isn't that waves are attenuated much more by
objects larger than their wavelengths. A 200m^2 sheet of paper will still
attenuate treble and be completely transparent to bass.

The real difference is that bass damping requires a combination of size, raw
mass, and permeability.

It's true that a tiny stick of a bass-damping material will do nothing to stop
bass, but it's also true that giant bass traps - like the ones used in studios
- will stop treble dead, but their effectiveness at bass frequencies depends
entirely on size, thickness, and the material they're made of.

A concrete wall has plenty of mass but no permeability, so it's a good
reflector at most frequencies. Bass traps use permeable materials like mineral
fibre which have no effect in thin slices, but they're made thick enough to
provide enough mass to damp the pressure oscillations.

~~~
saltcured
I believe that, at a fixed amplitude, the power level increases with frequency
for acoustic waves just like EM waves. Ultimately, this comes down to the area
under the sin wave. The energy density under the curve increases as you cram
more cycles into the same time interval.

Fixed amplitude is the important part here. Amplitude is not a perceptual
loudness nor a sound pressure measurement. Sound pressure measurements are
already a power scale and so two sounds with the same sound pressure carry the
same energy per unit time. Perceptual loudness is even more confusing, as it
applies a weighted curve to negate the non-uniform response of the human ear.
A higher sound pressure level in bass or very high frequency is required to
elicit the same perceived loudness as in our mid-frequency hearing.

Sound amplitude means the maximum particle displacement in one cycle, like the
maximum throw of a speaker diaphram. It is a distance, much like amplitude of
an electric signal is voltage. A woofer or tweeter with the same amplitude
would have the same throw! Those objectionable bass noises from downstairs
might involve a half inch or inch of displacement of a subwoofer. When is the
last time you saw a tweeter with a half inch of throw? I don't think that
would be blocked by tissue paper... it might melt your face off instead.

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ScottBurson
"Cancel 94%" sounds like a lot, but that's just -12dB — significant,
certainly, but nowhere near making audible sounds inaudible.

~~~
TheOtherHobbes
And it's very unlikely to be a broadband attenuator. Attenuating a single
frequency is a neat trick, but most acoustic applications require require
something that works a wide frequency range.

Given the breathless tone and the curious turns of phrase, I strongly suspect
the author has no background in sound, acoustics, science, or journalism.

~~~
xyzzy123
It could still be very useful without being wide-band!

Particularly with fan noise, there’s often one or two stand-out annoying
harmonics while the wide-band noise is less offensive.

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Mizza
I feel like a lot of the comments here are missing the point because this
isn't a magic noise-cancelling material.

The neat thing about this is that it works while still allowing air to flow
through. Even if it's not blocking broad spectrum sound, it's still useful to
block specific narrow frequency ranges. One immediate application mentioned in
the article is for drones, which are very loud. Maybe if you put these devices
below the fans of a drone, you could make it run much quieter.

It also establishes acoustic metamaterials as a new field of study, so we
could soon see significant improvements in this technology - imagine a dynamic
version of these rings which can change the frequencies which they block.

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intertextuality
Did... no one read the article before upvoting? This can reduce specific
frequency sounds by -12db, NOT 94% of "sound". Can /u/dang or someone edit
this clickbait title?

The wavelength of 100hz is 56.5 _feet_. While it may be possible that these
rings can attenuate _specific high frequencies_ , they don't [and cannot]
reduce all _sound_ in general. To say otherwise would be to defy physics.
Assuming the rings aren't vaporware, they could work for specific, constant
higher frequency sound sources, like machine hums as mentioned in the article.
However, the rings' aesthetic would be useless inside of an MRI machine...

There is a reason existing sound barriers aren't open, because even regular
walls block high frequencies. (And not just specific ones that match to a
ring's size). The best way to kill frequencies are thick objects (like walls).
For a room (like a editing studio or recording booth), it should have a non-
symmetrical wall with various recessed spaces to function as sound baffles, at
the least.

And lastly, these would be completely useless for low frequencies.

~~~
phasetransition
Minor pedantry: 10log(6/100) = -12.2, so you could sort of get the number
stated if you assume they meant sound power.

These metamerial, interference based approaches, are not going to be broadband
by the standards of physical acoustics.

This could be useful for helping cancel a particular harmonic of a helmholtz
resonator.

The real question, to me, is does it still work at high transitional Reynolds
numbers, or under full turbulent flow?

Source: End effects during transitional and turbulent flow for Helmholtz
resonators (i.e. bass reflex ports) in high output pro-sound loudspeakers has
been something I've played around with in the past.

~~~
hatsunearu
[https://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves](https://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves)

If one attempts to figure out what the subjective, perceived numerical volume
vs. actual dB SPL is for a large group of people, it roughly coincides with
the dB SPL number.

Bit more detail: you play a 100dB SPL tone and tell the participant "this is a
100" and play a 0dB SPL tone and tell the participant "this is a 0" and play
all kinds of other tones at various frequencies and sound pressures, you get
that curve. The unit for this arbitrary scale is called phon.

~~~
phasetransition
I am aware :-)

See ISO 226:2003

~~~
hatsunearu
Oh yeah, just putting it out there in case people wanted to know.

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lolc
The title of the article is incomplete. It should read

> An “acoustic metamaterial” that can cancel 94 percent of sound _at one
> frequency_.

I don't see how that could counter the turbulence generated by a jet engine.
Maybe that was just the journalist getting ahead of themselves.

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danjayh
The article implies that the test stand was running at a fixed frequency. This
makes me suspect that this has to be designed to interfere with transmission
of sound at a specific frequency, and perhaps isn't capable of eliminating
more complex sounds like voices or music.

~~~
lolc
Yes. If you click through to the paper you can see the frequency response
dipping around 460 Hz. Which is the frequency they're using in the demo.

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afarrell
As someone with disposable income working in an open office, I desperately
want to know if this can be used to build something to cancel out human voices
more completely than Bose QC-35s.

~~~
deegles
For voices you need passive sound isolation, not active noise cancelling. Try
these: Howard Leight by Honeywell Sync Stereo MP3 Earmuff (1030110), Black
[https://www.amazon.com/dp/B004U4A5RU/](https://www.amazon.com/dp/B004U4A5RU/)

They also give off a very strong “I’m busy” vibe

If that’s still somehow not enough, wear these concurrently (this is great for
planes too): Etymotic High-Fidelity Earplugs, ER20XS Standard Fit, 1 pair,
Polybag Packaging
[https://www.amazon.com/dp/B00RM6Q9XW/](https://www.amazon.com/dp/B00RM6Q9XW/)

Also recommend the above with these foam tips for longer wear, I’ve done up to
16 hours with only a little discomfort: Shure EABKF1-10M Medium Foam Sleeves
(10 Included/5 Pair) for E3c, E4c, E5c, E500PTH, i3c, i4c & SE Earphones
(Black)
[https://www.amazon.com/dp/B0015PN3W6/](https://www.amazon.com/dp/B0015PN3W6/)

~~~
porker
How about for lower frequencies: motorways, busy roads (no individual car
noises; a solid background roar)? They make having the window open here a
nightmare.

~~~
jfries
Isn't this exactly when active noise cancelling works the best?

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nicodjimenez
Like others here, I wonder how well this really works, but I applaud the
effort nonetheless and I hope to see progress in this area in the coming
years!

Better sound blocking tech would really improve people's lives and stress
levels, especially people who can only afford to live on busy streets in old
apartments without proper sound proofing. No to mention people who want to do
music in their apartments without bothering their neighbors.

~~~
incompatible
I'm not sure how you could use it for that. Well, you could put a couple of
those things over your ears, but earmuffs already exist. More likely it would
be useful for building better mufflers onto noisy equipment. A muffler on
musical instruments? I could imagine it fitted to a trumpet perhaps.

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mjmj
If affordable, all I can think about is how much this could help musicians or
bands that practice at home without disturbing the neighborhood.

~~~
lolc
If you want to feel the kick of your drum, your neighbours will hear it too.
This gadget won't help.

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m0zg
Too bad sound perception is logarithmic. 94% is nowhere near as much as one
would be led to believe if one did not know what a "decibel" is. Which is just
as well I suppose: makes for a very nice, clickbaity headline.

_Many_ people don't get this. People are surprised to discover that a 10W
guitar amp is not that much quieter than a 100W one, and even 1W amp can be
pretty darn loud, even though it's just 1% of the power.

~~~
edoo
-12dB on a drone could mean the difference between regulatory approval or not.

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chrismorgan
What does it mean to “cancel” or “block” “94% of sound”? From the paper’s
abstract: “Finally, the proposed unit-cell performance is validated
experimentally, demonstrating a reduction in the transmitted acoustic energy
of up to 94%.”

Does this basically mean amplification by about −12 dB?

~~~
tszyn
I guess so, but when you use energy instead of pressure, and a linear scale
rather than logarithmic, it makes the results look more impressive.

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rezreza
Just couple of points about the article. 1- the main focus of the study is to
silence the sound while maintaining ventillation, i think comparison with the
barrier is not relevant. 2- the structure is deep subwavelength compare to the
mufflers size 3- low frequency can still be silenced with this design but need
an stiffer material maybe metal 4- experiment is design considering both
fabrication limitation ( 3D print size) and the tube material to be
effectively work as a waveguide

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WilliamEdward
In physics we are learning about sound waves, and how noise cancelling
headphones detect noise and produce waves which are destructive to those
incoming sound waves, by matching the amplitude and sending them out at a
different time interval. I think future noise cancelling materials will make
use of some kind of tech like this.

I don't think materials that simply absorb sound are very efficient.

~~~
saagarjha
This, being an active process, would require energy would it not?

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hatsunearu
[https://journals.aps.org/prb/pdf/10.1103/PhysRevB.99.024302](https://journals.aps.org/prb/pdf/10.1103/PhysRevB.99.024302)

Anyone have access to this paper? This is driving me nuts and I want to know,
damn it :P

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tylerg
So what are the best, most creative ways to get rid of freeway/steeet noise
from your yard?

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petra
Is it possible to build this at home using a 3d printer ?

~~~
romwell
It appears that that's exactly how they made it.

What you end up with, though, is a pretty specific muffler.

Making a wall out of these blocks will take a while, and it'll only block a
narrow range of frequencies, somewhat.

But hey, it's better than plywood because you can, like, stick your hand
through it! And it's hi-tech!

~~~
sosuke
Sign me up! I’d love to muffle my GPU miners. They need air and make plenty of
fan noise.

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deytempo
It places the lotion in the basket...

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jaclaz
As a side note, I know that I am old (and grumpy) but was it really necessary
for the actual engineers to pose for the leading article picture?

I mean if it was a journalist's or editor's choice to _mis-_ illustrate the
invention creating a picture with models I would be fine with it, but the
actual engineers/inventors posing for it?

