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...
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.
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].
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).
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!
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.
"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."
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)
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.
You can attenuate treble with a sheet of toilet paper, but you need a lot of mass to stop bass of equivalent nominal level.
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.
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 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.
> 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.
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.
_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.
Does this basically mean amplification by about −12 dB?
I don't think materials that simply absorb sound are very efficient.
Anyone have access to this paper? This is driving me nuts and I want to know, damn it :P
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!
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?
Given the breathless tone and the curious turns of phrase, I strongly suspect the author has no background in sound, acoustics, science, or journalism.
Particularly with fan noise, there’s often one or two stand-out annoying harmonics while the wide-band noise is less offensive.
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)
https://www.bu.edu/research/files/2019/02/acoustic-metamater...
For more info, see https://simple.wikipedia.org/wiki/Decibel (which is much more approachable than https://en.wikipedia.org/wiki/Decibel).
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.
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.
Hence my criticism of the title.
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.
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.
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.
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.
[0] https://www.jdbsound.com/art/frequency%20wave%20length%20cha...
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/
Thus I use the audio-technica MSR7 at work. At home, I don't need isolation, so I enjoy sennheiser's HD600.
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.
That's why they are less capable in filtering non-repetitive noises like speech, especially their higher frequencies.
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.
The only down-side for me was that they are not as quick to pop on and off as regular headphones.
Recent studies are mixed as to which has a more deleterious effect on creativity, the coworkers yapping or the heavy metal.
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.
If so then perhaps the weighing of upvotes/downvotes should be adjusted to reflect that change in voting power?
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.
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.
See ISO 226:2003
Unfortunately.
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.
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.
The real difference is that waves are attenuated much more by objects larger than their wavelength.
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.
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.
