An “acoustic metamaterial” that can cancel 94 percent of sound(bu.edu)
bu.edu
An “acoustic metamaterial” that can cancel 94 percent of sound
https://www.bu.edu/research/articles/researchers-develop-acoustic-metamaterial-noise-cancellation-device/
98 comments
The article mentions using feno-like resonance to transform the frequency response (and phase). The effects of this are localized to a frequency-band around 440 Hz. Interestingly, this is a similar effect as mie-scattering.
Therefore, I am not sure the common knowledge of bass-traps and heavy materials for muffling sounds are actually applicable here.
I suggest reading the article and studying feno resonance.
Therefore, I am not sure the common knowledge of bass-traps and heavy materials for muffling sounds are actually applicable here.
I suggest reading the article and studying feno resonance.
It's Fano resonance.
And if I'm not mistaken, Fano resonances only work in a controlled environment like headphones (noise cancelling).
My comment wasn't a comment to the test in the article, but the expectations of the article - that any sound can be blocked, the writer is implying that this can be built into anything "a quieter world", which is not true for low frequencies which can't cancel itself out (without a very controlled environment like two subs of the same size in a cabinet, or an MRI machine) simply because it passes through objects and don't bounce.
I've seen noise cancellation concepts for the real world before, where a unit is placed on a window to cancel out outside noise by matching the vibrations of the sound.
In practice however, the sound waves are not predictable without a controlled environment, so it's just vaporware/concept [1].
[1] https://www.youtube.com/watch?v=Mv6sBuwzLhk
My comment wasn't a comment to the test in the article, but the expectations of the article - that any sound can be blocked, the writer is implying that this can be built into anything "a quieter world", which is not true for low frequencies which can't cancel itself out (without a very controlled environment like two subs of the same size in a cabinet, or an MRI machine) simply because it passes through objects and don't bounce.
I've seen noise cancellation concepts for the real world before, where a unit is placed on a window to cancel out outside noise by matching the vibrations of the sound.
In practice however, the sound waves are not predictable without a controlled environment, so it's just vaporware/concept [1].
[1] https://www.youtube.com/watch?v=Mv6sBuwzLhk
It's not a question of pressure; a wave has whatever pressure it has. It's a question of frequency (wavelength). Just like a flute can't make tuba sounds, a small one of these can't attenuate large wavelengths. But they make larger flutes that can play lower tones. Could you not just make one of these arbitrarily large to handle an arbitrarily low frequency?
> The most effective material is high mass and flexible, like cork or hemp crete.
Those materials work by providing a physical barrier. This invention is not comparable because it appears to allow air to flow down the pipe but (somewhat) prevents the sound. I guess it should be compared to the performance of acoustic ducting or inline silencers (ie like in a car exhaust).
Those materials work by providing a physical barrier. This invention is not comparable because it appears to allow air to flow down the pipe but (somewhat) prevents the sound. I guess it should be compared to the performance of acoustic ducting or inline silencers (ie like in a car exhaust).
That's why i mentioned bass-traps, which can be done with cheap PVC pipes in the corners of a room.
I still don't understand your point. In the scenario in the article, you've got some noise coming down a pipe and the invention attenuates it. By "PVC pipes in the corner of a room", it seems like you are talking about a way to remove resonant frequencies from a room - as some folks do to improve the acoustics of a room for a hi-fi setup. In the scenario in the article, the noise is in a pipe, not in a room.
I noticed that people assumed that this invention could block any sound, but it can only block specific frequencies, so that's why i pointed out that low frequencies can't be blocked - the test itself doesn't mention low frequencies.
It wasn't a complaint to the invention itself, which is certainly promising for blocking sounds in ventilation while keeping airflow.
PVC pipes trap low frequency sound by eating up it's energy and since low frequencies penetrate solid objects, resonant sound is what people are most annoyed by and those are reproduced in corners of a room - which is a good target for PVC bass traps to cancel out the bass.
When it comes to high frequencies, they bounce easier, so it's more about building a "maze" of surfaces for the sound to bounce on until it looses it's energy, which seems to be exactly what they do in the article, they keep bouncing the waves backwards until they die out and it's quite clever.
It wasn't a complaint to the invention itself, which is certainly promising for blocking sounds in ventilation while keeping airflow.
PVC pipes trap low frequency sound by eating up it's energy and since low frequencies penetrate solid objects, resonant sound is what people are most annoyed by and those are reproduced in corners of a room - which is a good target for PVC bass traps to cancel out the bass.
When it comes to high frequencies, they bounce easier, so it's more about building a "maze" of surfaces for the sound to bounce on until it looses it's energy, which seems to be exactly what they do in the article, they keep bouncing the waves backwards until they die out and it's quite clever.
My thought exactly. The problem with low frequencies is the large wavelength. The size of the damper needs to be roughly proportional to the frequency for reasons I don't remember.
If I had to guess I'd say that standing waves don't leave the chamber.
It will also capture only a limited volume.
> The mathematically designed, 3D-printed acoustic metamaterial is shaped in such a way that it sends incoming sounds back to where they came from, Ghaffarivardavagh and Zhang say.
That's certainly not what a sound engineer wants. The usecases are a little different, containing noise in an MRI machine (which has low freq rumbles) or away from ground for a drone. The word droning sound is probably not a chance homophone.
They can scale the structure as needed, so potentially for low frequs, and fit many next to each other to form a wall.
The helical structure in the ring is like a long winded pipe I guess? It's literally analogue to an electronic low pass filter from an inductor in series between source and ground, without a recipient. What a sound studio needs instead is a capacitor to ground in parallel to the recipient.
If I had to guess I'd say that standing waves don't leave the chamber.
It will also capture only a limited volume.
> The mathematically designed, 3D-printed acoustic metamaterial is shaped in such a way that it sends incoming sounds back to where they came from, Ghaffarivardavagh and Zhang say.
That's certainly not what a sound engineer wants. The usecases are a little different, containing noise in an MRI machine (which has low freq rumbles) or away from ground for a drone. The word droning sound is probably not a chance homophone.
They can scale the structure as needed, so potentially for low frequs, and fit many next to each other to form a wall.
The helical structure in the ring is like a long winded pipe I guess? It's literally analogue to an electronic low pass filter from an inductor in series between source and ground, without a recipient. What a sound studio needs instead is a capacitor to ground in parallel to the recipient.
I'd need to some more research material to confirm this but I wanna say that the structure seems to exploit some effects that you can't reason with lumped model + T-line models.
In what world is anyone using PVC to make bass traps? Every advice I have seen uses rockwool or something like Owens Corning 703/705. I am assuming you are not referring to the structure used to contain the acoustic material.
Thank you for posting about the bass trap, I had never heard of it before and am enjoying spending time learning about it (and the other sound-dampening materials you mentioned)
This makes me wish I could put some bass traps in the wall between one neighbour and me, and something like hemp crete to drown out the sound of the screaming kids from another neighbour!
This makes me wish I could put some bass traps in the wall between one neighbour and me, and something like hemp crete to drown out the sound of the screaming kids from another neighbour!
By all means, read up on bass traps... but be aware that posts about bass traps imply a fundamental misunderstanding of what they do (perhaps I'm misreading).
The problem: a speaker in a room produces sound, that sound is reflects by the walls. Those reflections will vary WRT phase of the original sound and causing something called comb-filtering (some frequencies will be louder because the reflections are in phase and amplify -- others will be 180º out of phase, resulting in a complete cancellation of those frequencies).
Solutions: sound attenuating material at the edges of a room to interfere with the _reflections_ and this reduce or eliminate comb-filtering. The goal is to improve the listening experience _inside_ the room. Acoustic treatment does almost nothing to help your neighbours.
The problem: a speaker in a room produces sound, that sound is reflects by the walls. Those reflections will vary WRT phase of the original sound and causing something called comb-filtering (some frequencies will be louder because the reflections are in phase and amplify -- others will be 180º out of phase, resulting in a complete cancellation of those frequencies).
Solutions: sound attenuating material at the edges of a room to interfere with the _reflections_ and this reduce or eliminate comb-filtering. The goal is to improve the listening experience _inside_ the room. Acoustic treatment does almost nothing to help your neighbours.
The article mentions on one hand a high pitched note, but on another hand enough bass to see the subwoofers play it:
"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."
"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."
I assumed that this was the interviewers observation and not a fact, because even a mid-range driver would be moving visibly.
Considering the size of the tube, this is certainly not a driver big enough to go to lower frequencies.
(Specialized drivers at 4" can go down to 25hz though)
Considering the size of the tube, this is certainly not a driver big enough to go to lower frequencies.
(Specialized drivers at 4" can go down to 25hz though)
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.
To get the same (perceived) amplitude a low freuquency wave needs much more power than a higher frequency one. In a speaker most power is used in the low end while the tweeters use just a fraction of it.
This means that given any kind of regular music played on this speaker the created air pressure differences will be much higher for the bass frequencies than for the treble frequencies.
On top of that the difference in wave length also changes how it interacts with materials. The long bass wave bends around corners and goes through walls (which is why you can hear them two rooms over), while the shorter treble wave is bascially reflected by even a thin wall and looses energy fast in free air.
This means that given any kind of regular music played on this speaker the created air pressure differences will be much higher for the bass frequencies than for the treble frequencies.
On top of that the difference in wave length also changes how it interacts with materials. The long bass wave bends around corners and goes through walls (which is why you can hear them two rooms over), while the shorter treble wave is bascially reflected by even a thin wall and looses energy fast in free air.
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.
You can attenuate treble with a sheet of toilet paper, but you need a lot of mass to stop bass of equivalent nominal level.
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.
The real difference is that waves are attenuated much more by objects larger than their wavelength.
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.
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.
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.
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.
That guy might have tried to say that lower frequencies cause more displacement for the same SPL, which means they necessarily go through materials a lot better.
edit: in more detail, the pressure is basically analogous to force in a fluid, and particle displacement is analogous to well, displacement, and since F=ma or F=mx'', for a given amount of pressure, the acceleration of particles stay constant, so for sinusoidal displacements you end up needing more displacement to get the same SPL for lower frequencies. And the falling sensitivity of the human ear at lower frequencies make this even more pronounced.
edit: in more detail, the pressure is basically analogous to force in a fluid, and particle displacement is analogous to well, displacement, and since F=ma or F=mx'', for a given amount of pressure, the acceleration of particles stay constant, so for sinusoidal displacements you end up needing more displacement to get the same SPL for lower frequencies. And the falling sensitivity of the human ear at lower frequencies make this even more pronounced.
I am surprised to read that you were downvoted by some. Even if you are completely wrong (I have no idea, I am not a sound engineer), you are trying to provide an opinion and I would simply debate it with you, rather than downvoting.
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Lately, I have noticed a lot more downvoting going on than I was used to. Maybe a confirmation bias on my part, but sad nevertheless... I'd use downvoting only for submissions that are harmful.
The longer this website is around, the more people there will be with enough karma to be able to downvote in the first place. Perhaps that explains the shift you've seen?
If so then perhaps the weighing of upvotes/downvotes should be adjusted to reflect that change in voting power?
If so then perhaps the weighing of upvotes/downvotes should be adjusted to reflect that change in voting power?
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.
I've found that musician earplugs under ear defenders essentially cancels all sound, including human voice.
It's not something I would recommend. It makes me feel uneasy. A dozen people could walk up behind you and watch you work, and you'd never know until they tapped you on the shoulder. If you have any anxiety at all about this, true silence will make it far, far worse.
Noise isn't the only problem with open office layouts. It's just a convenient way to describe it to people who don't understand. If you think it's hard to talk to business people about the problems caused by excessive sound levels, imagine how difficult it is to talk to them about how you feel.
At some level, though, they do know this. Your CEO doesn't have his desk facing the door of his office because that position is the quietest. Try do-si-do'ing his desk one day and see how long that lasts.
It's not something I would recommend. It makes me feel uneasy. A dozen people could walk up behind you and watch you work, and you'd never know until they tapped you on the shoulder. If you have any anxiety at all about this, true silence will make it far, far worse.
Noise isn't the only problem with open office layouts. It's just a convenient way to describe it to people who don't understand. If you think it's hard to talk to business people about the problems caused by excessive sound levels, imagine how difficult it is to talk to them about how you feel.
At some level, though, they do know this. Your CEO doesn't have his desk facing the door of his office because that position is the quietest. Try do-si-do'ing his desk one day and see how long that lasts.
What you’re looking for is a Bose QC-35s... playing Metallica.
Recent studies are mixed as to which has a more deleterious effect on creativity, the coworkers yapping or the heavy metal.
Recent studies are mixed as to which has a more deleterious effect on creativity, the coworkers yapping or the heavy metal.
Careful with those Bluetooth headphones, a colleague of mine managed to pair her laptop with her speakers rather than her 'phones, and then promptly proceeded with listening to a (veee-eeery) adult audiobook.
Apparently, it can be quite difficult to determine whether the sound comes from your phones or outside them if you haven't turned the NC on.
Fifty shades of embarrassing moments, that.
Apparently, it can be quite difficult to determine whether the sound comes from your phones or outside them if you haven't turned the NC on.
Fifty shades of embarrassing moments, that.
I just got a pair, every time I start music I tend to mute it and slowly increase volume until I am sure where it comes from.
I have a pair and I can attest to that.
Unfortunately.
Unfortunately.
That is my current strategy, though I’ve been using The Hu on repeat lately.
The trick with this material is that it pretty much reflects sound waves. On the way back, these reflected sound waves then crash into the upcoming soundwaves and they cancel each other out.
Headphones with active/acoustic noise cancelling use the same trick, except that they pick up the upcoming sound waves with a microphone and then use a speaker to generate those "reflected" soundwaves.
Actually-reflected soundwaves cannot be as strong as the upcoming soundwaves, so they're never going to fully cancel out the noise. Those generated soundwaves can.
One point is that there's most likely less latency for a soundwave to get reflected vs. picked up by a microphone and then generated by a speaker. However, to my knowledge our human senses have even more latency than both of those, so I don't think that matters.
Headphones with active/acoustic noise cancelling use the same trick, except that they pick up the upcoming sound waves with a microphone and then use a speaker to generate those "reflected" soundwaves.
Actually-reflected soundwaves cannot be as strong as the upcoming soundwaves, so they're never going to fully cancel out the noise. Those generated soundwaves can.
One point is that there's most likely less latency for a soundwave to get reflected vs. picked up by a microphone and then generated by a speaker. However, to my knowledge our human senses have even more latency than both of those, so I don't think that matters.
Don't extrapolate our slow reaction time to mean more than just that! :) Low latency still matters. Think about latency when scrolling/dragging on a touch screen for example. There's a large difference in feel depending on latency, even if the latency is lower than your reaction time.
The latency in the active noise-cancelling systems is a few milliseconds, mostly due to processing time.
That's why they are less capable in filtering non-repetitive noises like speech, especially their higher frequencies.
That's why they are less capable in filtering non-repetitive noises like speech, especially their higher frequencies.
This is a very bad meme that's been propagated so much across the internet.
1. The latency is active noise cancelling systems is very low; much less than the frequency of most sounds.
2. Noise cancelling is ineffective at higher frequencies because the space between the speaker driver and the ear becomes large enough that the destructive interference becomes imperfect.
3. The feedback has to come from somewhere, and once the frequencies become high enough, the phase shift caused by the physical distance between the driver and microphone start to affect the feedback loop.
4. Because of these issues at higher frequencies, they just lower the feedback gain at higher frequencies. This effectively makes the active noise cancellation system be not sensitive to higher frequencies.
5. This is very much akin to frequency compensation in other topics like buck converters and op amps--the additional phase shift in the feedforward path that often increases as frequency goes up becomes problematic to compensate, so they just make the feedback loop insensitive to that region.
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the quick way to debunk this is two tests:
1. Play some bandlimited noise (https://www.youtube.com/watch?v=5qV5j9wD5e8) really loudly and I guarantee you any shitty ANC headphone will cancel this out just fine. Noise by definition is non-repetitive.
2. Play a high frequency sinusoid (https://www.youtube.com/watch?v=TRKB5kWs7KE) really loudly and it will go straight through any ANC headphone. A sinusoid is as repetitive as it gets.
1. The latency is active noise cancelling systems is very low; much less than the frequency of most sounds.
2. Noise cancelling is ineffective at higher frequencies because the space between the speaker driver and the ear becomes large enough that the destructive interference becomes imperfect.
3. The feedback has to come from somewhere, and once the frequencies become high enough, the phase shift caused by the physical distance between the driver and microphone start to affect the feedback loop.
4. Because of these issues at higher frequencies, they just lower the feedback gain at higher frequencies. This effectively makes the active noise cancellation system be not sensitive to higher frequencies.
5. This is very much akin to frequency compensation in other topics like buck converters and op amps--the additional phase shift in the feedforward path that often increases as frequency goes up becomes problematic to compensate, so they just make the feedback loop insensitive to that region.
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the quick way to debunk this is two tests:
1. Play some bandlimited noise (https://www.youtube.com/watch?v=5qV5j9wD5e8) really loudly and I guarantee you any shitty ANC headphone will cancel this out just fine. Noise by definition is non-repetitive.
2. Play a high frequency sinusoid (https://www.youtube.com/watch?v=TRKB5kWs7KE) really loudly and it will go straight through any ANC headphone. A sinusoid is as repetitive as it gets.
Since you mention disposable income, if you can tolerate in-ear monitors I would suggest getting custom-fit silicone IEM. Used with even a very low level of music (or even some white noise generator) they dampen noise like nothing else in my experience. Successfully tested in a work environment with endless yammering, bleeping computer equipment, that mandatory 'shout-speaking' colleague, and even once a guy who let a 1U server running on his desk for a week for testing purposes (because why not).
The only down-side for me was that they are not as quick to pop on and off as regular headphones.
The only down-side for me was that they are not as quick to pop on and off as regular headphones.
Not a fan of the QC-35. I find their ANC headache-inducing, and while the overall sound signature is very good, it's only because of built in DSP doing EQ. The distortion is unbearable.
Thus I use the audio-technica MSR7 at work. At home, I don't need isolation, so I enjoy sennheiser's HD600.
Thus I use the audio-technica MSR7 at work. At home, I don't need isolation, so I enjoy sennheiser's HD600.
Earplugs under the headphones?
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/
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/
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/
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/
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/
I've had these for a year and like them: Professional Safety Ear Muffs by Decibel Defense:
amazon.com/gp/product/B01BEENYCQ/
Active noise cancelling is overrated. Use passive isolation.
No, -12db is inferior to most earplugs.
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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?
Does this basically mean amplification by about −12 dB?
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.
It places the lotion in the basket...
"Cancel 94%" sounds like a lot, but that's just -12dB — significant, certainly, but nowhere near making audible sounds inaudible.
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.
Given the breathless tone and the curious turns of phrase, I strongly suspect the author has no background in sound, acoustics, science, or journalism.
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.
Particularly with fan noise, there’s often one or two stand-out annoying harmonics while the wide-band noise is less offensive.
The author is probably one of those science journalist that has a at best shaky grasp of the material--these people have to write appealing articles (they're basically advertising the university) for a whole lot of different disciplines, so it's not going to be easy.
And I think the point is that this blocks out only certain frequencies, without being a massive structure (you can easily make a serpentine acoustic notch filter but it's gonna be huge)
And I think the point is that this blocks out only certain frequencies, without being a massive structure (you can easily make a serpentine acoustic notch filter but it's gonna be huge)
And for comparison, a single 4mm pane of glass is about -27db, and cheap commodity wall board is about -46db (https://www.insulationsuperstore.co.uk/product/soundboard-3-...)
For those of you who haven't yet read the article, the cool thing about this new technology is that the material is not a solid plane, but an empty ring that allows air to pass through:
https://www.bu.edu/research/files/2019/02/acoustic-metamater...
https://www.bu.edu/research/files/2019/02/acoustic-metamater...
So, essentially, they invented a silencer/muffler?
Certainly interesting, but the applications of that would be somewhat niche.
To be specific, there are not that many scenarios where a solid wall won't do, but a honeycomb-like barrier is OK. Aesthetics are important, but musicians in a studio couldn't care less about how stuff looks as long as it works (and so do your musicians' neighbors).
One good application, as others have mentioned, is putting that thing around a fan, to minimize noise (a solid barrier defeats the purpose of a fan). I wonder what else would be a killer feature application of this kind of structure.
Certainly interesting, but the applications of that would be somewhat niche.
To be specific, there are not that many scenarios where a solid wall won't do, but a honeycomb-like barrier is OK. Aesthetics are important, but musicians in a studio couldn't care less about how stuff looks as long as it works (and so do your musicians' neighbors).
One good application, as others have mentioned, is putting that thing around a fan, to minimize noise (a solid barrier defeats the purpose of a fan). I wonder what else would be a killer feature application of this kind of structure.
I know nothing about acoustics and its units - the abstract of actual paper says more precisely that it reduces the 'acoustic energy' by 94%, not the power. Can you convert this to a decibel figure? Would you mind explaining what these units mean and how you do the conversions?
It’s a logarithmic scale, which is reasonably approximated as an increase of 3 dB doubling the power (“acoustic energy” is synonymous). A 94% reduction means you’ve reduced it to 6% of the original, which is about a 12 dB reduction (you can figure it in your head like so: 3 dB = 50%, 6 dB = 25%, 9 dB = 12.5%, 12 dB = 6.25%).
For more info, see https://simple.wikipedia.org/wiki/Decibel (which is much more approachable than https://en.wikipedia.org/wiki/Decibel).
For more info, see https://simple.wikipedia.org/wiki/Decibel (which is much more approachable than https://en.wikipedia.org/wiki/Decibel).
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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.
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.
> 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.
Is it possible to build this at home using a 3d printer ?
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!
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!
Sign me up! I’d love to muffle my
GPU miners. They need air and make plenty of fan noise.
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.
_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.
-12dB on a drone could mean the difference between regulatory approval or not.
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.
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.
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.
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?
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?
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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.
I don't think materials that simply absorb sound are very efficient.
This, being an active process, would require energy would it not?
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.
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.
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.
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.
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.
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.
I am aware :-)
See ISO 226:2003
See ISO 226:2003
Oh yeah, just putting it out there in case people wanted to know.
The pedantry is absolutely correct; however most people (aka anyone who hasn't studied acoustics, etc) do not understand the differences in how it's measured. If you just say "this reduces sound by 94%" to a layperson they would assume it to mean "this makes something nearly quiet by reducing its volume by 94%".
Hence my criticism of the title.
Hence my criticism of the title.
Isn't the wavelength of 100 Hz 11.25 feet? Am I missing something?
Yes, I apologize. I wrote 100hz but I meant 20hz, which is 56.5 ft. [0]
[0] https://www.jdbsound.com/art/frequency%20wave%20length%20cha...
[0] https://www.jdbsound.com/art/frequency%20wave%20length%20cha...
A useful application would be e.g. in cases where you want to target specific frequencies AND airflow should be possible.
So this could be useful for attenuating small computer fans by 12 db without or adding meandering pipes filled with absorbing foam.
For general acoustics I'd stick to a accuratly calculated and well built diaphragmatic absorber or at least a helmholtz absorbers.
So this could be useful for attenuating small computer fans by 12 db without or adding meandering pipes filled with absorbing foam.
For general acoustics I'd stick to a accuratly calculated and well built diaphragmatic absorber or at least a helmholtz absorbers.
>Did... no one read the article before upvoting?
Maybe. Probably. I'll upvote a headline so it ends up in my "upvoted submissions" list so that I can peruse that list and read things later that looked interesting. Then I'll unvote if I didn't like it.
No, I have not yet adapted to the 'favorite' link.
Maybe. Probably. I'll upvote a headline so it ends up in my "upvoted submissions" list so that I can peruse that list and read things later that looked interesting. Then I'll unvote if I didn't like it.
No, I have not yet adapted to the 'favorite' link.
-12 dB is 94%. 12 decibels is 1.2 bels.
10^(-1.2) = 0.063 so 12 dB down means intensity is reduced to 6.3%, or by 93.7%.
-12 dB is a worthwhile cut if it can be achieved with a barrier that has some good qualities: being unobtrusive, reasonably light-weight, thin, cost effective, perhaps transparent or translucent, etc.
If you double it up, -24 dB may be possible.
Stopping sounds in higher frequency ranges has applications. It won't block your neighbor's thumping bass, but there are other situations that benefit from noise blocking, like appliances with motors.
10^(-1.2) = 0.063 so 12 dB down means intensity is reduced to 6.3%, or by 93.7%.
-12 dB is a worthwhile cut if it can be achieved with a barrier that has some good qualities: being unobtrusive, reasonably light-weight, thin, cost effective, perhaps transparent or translucent, etc.
If you double it up, -24 dB may be possible.
Stopping sounds in higher frequency ranges has applications. It won't block your neighbor's thumping bass, but there are other situations that benefit from noise blocking, like appliances with motors.
Because of these click-bait titles I am jumping to comments directly to see the validity of articles and I know I am not alone. This actually hurts submissions that are front page worthy.
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.02...
Like you said, it’s not wideband. This implementation is a notch filter about 50Hz wide. Interesting if you’re looking to reduce a specific source, which can happen. For example to cancel fan noise.
Like you said, it’s not wideband. This implementation is a notch filter about 50Hz wide. Interesting if you’re looking to reduce a specific source, which can happen. For example to cancel fan noise.
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
Anyone have access to this paper? This is driving me nuts and I want to know, damn it :P
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
So what are the best, most creative ways to get rid of freeway/steeet noise from your yard?
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.
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.
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...