[tmikaeld]

As far as deep bass goes, this won't hinder that - since bass waves have too high of a pressure to not pass through the object.

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

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

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

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

[1] https://www.acousticfields.com/how-do-you-stop-low-frequency...

[edejong]

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.

[tmikaeld]

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

[Gatsky]

It's Fano resonance.

[rdiddly]

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?

[abainbridge]

> 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).

[tmikaeld]

That's why i mentioned bass-traps, which can be done with cheap PVC pipes in the corners of a room.

[abainbridge]

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.

[tmikaeld]

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.

[posterboy]

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.

[hatsunearu]

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.

[vonseel]

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.

[bloopernova]

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!

[georgn]

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.

[fulafel]

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."

[tmikaeld]

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)

[IshKebab]

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

[atoav]

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.

[TheOtherHobbes]

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

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

[hexane360]

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

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

[TheOtherHobbes]

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

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

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

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

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

[saltcured]

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

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

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

[hatsunearu]

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.

[simonebrunozzi]

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.

[BossingAround]

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.

[vanderZwan]

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?