Hacker News new | past | comments | ask | show | jobs | submit login
Engineers create synthetic, sound-silencing structure that blocks 94% of sounds (eurekalert.org)
121 points by fezz on July 7, 2019 | hide | past | favorite | 45 comments

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.

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

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.

Probably. Still, it's something to cure fan noise, maybe a couple of harmonics -- not the sort of thing that will work on speech.

This paper came out last year and was on HN https://www.researchgate.net/publication/327274462_A_Review_...

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...

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

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.

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.

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.

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

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.

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.

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?

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.

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"

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.

Acoustic foam? As I understand it, plain old fiberglass or rock wool batts are considerably more effective as acoustic material in a stud bay.

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...

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

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

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.


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.

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.

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.

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

Could it be used to quiet a submarine turbine?

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.

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??

Here it is https://www.thingiverse.com/thing:3575092 I'm going to try it myself.

Not broadband sound, right?

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.

Ok, we've changed from https://www.fastcompany.com/90316833/scientists-have-discove... 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.

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.)

Sure, done now.

Its fun beating up journalists, but the examples they give are exactly the ones that appear in the press release, which has direct quotes about them from the scientists.


So in this case, if you have a bone to pick, it's not with the journalist.

> the examples they give are exactly the ones that appear in the press release,

That's not true. For example, The Fast Company article says "they could be stacked to build soundproof yet transprent walls. Cubicles will never be the same." The press release doesn't include that. This makes sense because it ties in to the emotionally charged reference to "your coworkers" in the title, which is not a trick that the press release pulls.

More significantly, the Fast Company article is written in a cloying hyperbolic style while the press release is pretty neutral. And the titles are beyond comparison, which is probably the most significant thing because titles have the greatest influence on discussion. Many readers have developed allergic reactions to titles like "Scientists have discovered a shape that blocks all sound–even your co-workers", which insult the intelligence so badly.

What's interesting is how the journalistic outlet has to be so much more exaggerated and use so many more tricks even than a press release. Presumably this reflects the economics of media vs. that of universities.

So, if the main complaint is hyperbole over the ability to build cubicles that block office noise, I would draw your attention to this passage from the press release

> Ghaffarivardavagh and Zhang also point to the unsightliness of the sound barriers used today to reduce noise pollution from traffic and see room for an aesthetic upgrade. "Our structure is super lightweight, open, and beautiful. Each piece could be used as a tile or brick to scale up and build a sound-canceling, permeable wall," they say.


> "When we want to create a wall, we will go to a hexagonal shape" that can fit together like an open-air honeycomb structure.

> Such walls could help contain many types of noises. Even those from the intense vibrations of an MRI machine, Zhang says.

Nothing there suggests that the journalists were indulging in hyperbole, although they were clearly being light hearted. However, the comment to which I originally replied seemed to be indulging in hypobole.

I'd say the main complaints were the cloying text and the infantilizing title. Many HN readers find these things more than a little annoying, and this was a particularly strong case.

Your quotes don't mention anything about office noise, cubicles, or coworkers. Why would they add those in? Presumably to make the content more sensational, since that's the effect it has.

"What's interesting is how the journalistic outlet has to be so much more exaggerated and use so many more tricks even than a press release. Presumably this reflects the economics of media vs. that of universities."

This really depends on the media outlet. Some, like Fast Company are full of uncritical puff pieces about the industry they cover, others not so much.

Economics certainly play a role, however -- from media being soft on their advertisers to industry execs writing for, editing, owning, or having input on hiring/firing decisions to certain media outlets pandering to the lowest common denominator and deliberately writing the most hyperbolic, sensationalistic articles to be popular with readers fond of that sort of fare and outcompete other media that aren't quite as sensationalitic. It's a winning formula, as can be witnessed by the widespread success of tabloids.

Not all media is like this, though.

Audiophile site: New revolutionary "Ring of Silence" device will block any unwanted sound, turning any noisy living room into a listening experience out of this world. Better coupled with our deionized cork earpads at just €999.99.

Well, honestly, that’s actually a fine use case here. Good idea! If you build them on a screw thread, and bolt them onto open-ear headphones, then you absolutely could block any unwanted sound’s key frequencies until it’s knocked down into the background noise. You’d only be able to negate the one sound, but for a lot of people, that’s a dream come true.

Calling FastCompany journalism is like calling McDonald’s a restaurant (I enjoy both from time to time!)

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

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

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact