Moth wing–inspired sound absorbing wallpaper in sight after breakthrough | Hacker News Reader

Moth wing–inspired sound absorbing wallpaper in sight after breakthrough

phys.org

120 pointsthedday37 comments

I thought I had understood moths vs bats a long time ago.

Then I read https://steveblank.com/2009/03/23/if-i-told-you-i%E2%80%99d-... after watching Steve Blank's amazing talk on the Secret History of Silicon Valley. (About an hour long, see https://www.youtube.com/watch?v=ZTC_RxWN_xo, and well worth it.)

Yeah, moths are designed to be hard to echolocate. But bats find them anyways. The moth knows the bat is coming - they have ears as well. And finally the moth rubs its legs together, making a loud sound to deafen the bat, and then randomly dodges.

The bat knows the moth will do this, but has to guess which way at the critical moment, so only gets the moth half the time.

Are there moths that have evolved the Panenka, making the sound, but not dodging at all (https://en.wikipedia.org/wiki/Panenka_(penalty_kick))?

Can’t the moth dodge in more than two directions?

You can often trigger this dodging reflex in moths with a simple broadband ultrasound generator: quick jingling a keychain of metal keys. A nearby moth will drop suddenly when it detects the "echolocation pulse" with its tympanic membrane.

The counter-counter-evolutionary strategy of moth-specialist bats is to "whisper", and bats of the genus Corynorhinus for example have comically large ears so that they can echolocate at very low amplitude in "stealth mode", avoiding detection by moths until the very final approach phase.

I'm not familiar with moths producing an active "jamming" signal, and have a hard time believing it'd be very successful given that bats often produce echolocation signals as loud as 110dB (though they drop amplitude and refine frequencies as distance to a target decreases), but my experience is exclusively with US bats.

Another problem with announcing that you're searching for and homing in on food at 110dB is that any other bats nearby can hear as well. I've recorded Tadarida producing a sinusoidal FM jamming signal to try and prevent a competitor from success.

Just from listening to the bats; it sounds to me like they spend at least as much time cussing at each other as they do pinging. I wonder how much information the bats gather from others' ping calls and also from the "other chatter" a crowd of bats produces.

Interesting, this reminded me of something I watched long ago about bat-moth interactions.

According to this documentary[1], the Tiger moth has it's own "siren" that "warns bats that it is poisonous", however upon further research I came across this article[2] which claims that it is indeed sonar jamming. Thought I'd share.

aside: it's amazing that I could find Alien Empire online.

[1]https://archive.org/details/AlienEmpireBattlezoneMetropolis

(the bat-moth part is just after 13:00)

[2]https://www.scientificamerican.com/article/sonar-jamming-tig...

Maybe not “wallpaper”…

”… with the scale layer being only 1/50th of the thickness of the wavelength of the sound that they are absorbing…”

The scales work in the ultrasonic range. Bats are 30-50kHz if I recall, maybe higher.

The oboe tuning the orchestra is ~440Hz which is a 75cm wavelength, so a “wallpaper” a bit thicker than a centimeter. Tuning for power line hum or traffic rumble will make the wallpaper about as thick as a banana is long.

This could be an interesting tech for lower-power/lighter noise-cancelling headphones: a layer of metamaterial to dampen the higher frequencies, and active electronics for the remainder. I imagine there's _some_ of this already going on in the high-end headphone space, but lighter and longer-lasting headphones are always welcome.

I think if you used this in the original design, a banana length is nothing for the reward of total silence.

Similarly the 87% is impressive, but that translates to a difference of "only" 9 dB. The way our ears work makes me wonder if that is enough to make a difference for noise reduction (my earplugs say on the package they reduce sound by 32 dB, for example)

edit: of course, worst case it would still contribute passively to noise reduction

Yesterday I walked along a busy road with a decibel meter app and as I went behind a sound-absorbing wall, the level went down around 10dB.

The difference was significant and it felt as if the road was one block away.

Right, so it would still be less stress-inducing at least.

Worst case you just add more layers, like we do with sound absorbers now.

If some kind of moth wing inspired metamaterial can shrink the width of broadband sound absorbing panels by 10x that would be quite useful still.

Good points, it hopefully will lead to metamaterials that are at least better than currents solutions

Decibel is a logarithmic scale

Yes, and also a relative scale like percentages are. A change of 87% is about nine decibels. If earplugs need to be 30+ decibels that makes me wonder if nine decibels is enough to have a significant impact (but another comment suggests it does)

I don't think it's as simple as scaling with wavelength, although I would be happy to be proved wrong: https://news.ycombinator.com/item?id=31769803#31790292

Paper: https://royalsocietypublishing.org/doi/epdf/10.1098/rspa.202...

Their graphs are from 20kHz to 160kHz (at a quick skim), so this doesn’t appear to be an immediately useful breakthrough. Some graphs show the scales are mostly tuned to a frequency, not wideband, so even more limited. Very cool science though.

There are aspects of it that should scale, but it's not as simple as "multiply up with the wavelength". They mention that the layer of air is significant, and that makes me think the Reynolds number comes into it. My guess is that the high viscosity of air at the scale of the scales makes it a fairly effective medium for getting rid of the energy as the scales vibrate. If you just make bigger scales the air appears correspondingly thinner, so there's less viscosity, so the scales wouldn't be damped as quickly. You'd want some other sort of damping mechanism to dump the kinetic energy into heat. But other than that, the main challenge is getting the scales to have the right harmonic characteristics, which is just a matter of shape and stiffness.

Nanolayr has a developed product (spun nano-fibres) that has ridiculous acoustic performance for its thickness/weight. The path to market for these sorts of product is long.

https://www.nanolayr.com/product/sonolayr/

It’s fascinating to learn about how deep the game of cat and mouse goes. It gives me deep appreciation for evolution and long timescales.

This would be a game changer for living in apartments, please expedite this as an affordable material

This is for reducing reflected sound, not transmitted sound. We already have building technologies to block transmitted sound. People just usually choose not to pay extra because it's not actually that important to them.

What materials are commonly used? People in older buildings definitely have sound issues

I was told lowering they ceiling and creating an air gap is effective

Usually thick insulation because you need mass to block bass.

Like rockwool: https://www.rockwool.com/north-america/products-and-applicat...

It’s really difficult, especially in the bass region. Things like double acoustically isolated walls that are really expensive.

In my experience it's newer buildings that tend to have paper thin walls. In my current apartment(late 70s) I very rarely hear my neighbors.

At my last apartment I could literally hear my neighbors cough. Absolutely miserable. I wish there were some sort of measurable standard rating for noise transmittance through walls that landlords are obligated to disclose to potential renters.

New buildings have strict fire separation requirements that pretty much enforces sound proofing. All new build high rises I have stayed in have had total silence.

Seen many buildings where the concrete walls soundproof the rooms but plumbing ducts in bathrooms transmit sound like crazy - as in you can hear conversations from people several floors down. The inspection hatch cover made of thin sheet metal seems to act like a microphone exciting the air in the duct causing the other covers to act like speakers

Poured concrete, or whatever you might do that is as close to thick, airtight, poured concrete barriers as possible.

Eliminate all holes, and it just becomes a question of mass.

Mass Loaded Vinyl Soundproofing

I think when you say people you mean “builders.” I think people, I.e., the people who actually live in the homes, prefer quiet.

* People just usually choose not to pay extra because it's not actually that important to them*

Do they choose this, though? Or are they either renting (absolutely no choice) or not monied enough to upgrade their house in this way? Is this something that your average builder offers the average person building a home? (My parents didn't have that choice when building a house in the 90s)

The technologies involved in providing inter-room sound isolation aren't exotic/unknown in general (due to significant demand from some types of office-style commercial buildings and upscale/premium apartments/condos), nor do they exceed the familiar capabilities of your normal stud-framed wall crew that regularly does insulated exterior/garage-facing walls.

So as long as you're in a place where common construction crews have regular experience building thermally insulated stud-framed walls, you'd at most have to look for an architect that has experience designing cross-tenant sound isolation who is otherwise a suitable choice for designing the kind of home you desire.

Their existing experience allows to get decent economics for the design workload of even your one-off non-catalogue customization. And considering there are few differences between sound isolation and thermal isolation (except that heat can also be stopped by IR-opaque foam rolling in for air pressure in the evacuated space between two foils (AFAIK that is much better at shielding heat flux than sound's pressure waves, due to the inherent concentration of air pressure into the stiff foam, as there is no gas pressure inside the pores to handle static air pressure forces, while heat conduction doesn't focus like it and heat radiation is interrupted by the opaque foam walls that act as "vacuum super insulation"[0]), and sound can also be stopped by thick heavy stone walls), the architect would at most spec slightly different insulation and likely somewhat different mounting brackets/pads for connecting the drywall to the frame.

The end result is no need for non-trivial engineering that a local architect should be able to satisfyingly do from experience, and a design that is just a little weird in overall layout/structure, instead of exceeding the construction crew's scope of experience in any particular detail.

[0]: https://en.wikipedia.org/wiki/Multi-layer_insulation

It's both, isn't it? The paper talks about measuring the effect of having both the front and the back bare or coated.

> The potential to create ultrathin sound absorbing panels has huge implications in building acoustics. As cities get louder, the need for efficient non-intrusive sound mitigation solutions grows. Equally, these lightweight sound absorbing panels could have huge impacts on the travel industry, with any weight saving in planes, cars and trains increasing efficiency in these modes of transport and reducing fuel use and CO2 emissions.

I predict it would become a moral hazard i.e. that people will live less quietly because they reason that the soundproofing means they can be noisy, and the extra noise will slip through, a form of Jevons paradox. I also see the extra efficiency they bring up will also be eaten up by increased use. Again, Jevons paradox rears its head.

I do wonder, however, if it would lead to completely new products, not just better versions of what we have, things we could only imagine at this point.

Disagree. There are already substantial differences between noise isolation in different apartments, but that does not lead to better isolated locations being louder. It is usually the opposite, i.e. what one would naively expect.

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