Comments
starnutq163 t1_j2cyqo8 wrote
Please do get into superposition
SippyTurtle t1_j2d2evd wrote
At least take me out to dinner first.
Newme91 t1_j2dbtbe wrote
Bite the pillow Petal, I'm coming in dry!
[deleted] t1_j2dgdij wrote
[removed]
OverlordPoodle t1_j2dv1i8 wrote
>Bite the pillow Petal, I'm coming in dry!
Is that you Slap on Titan Levi?
JB_smooove t1_j2dani6 wrote
Buy me a few drinks at least.
frzx1 t1_j2di665 wrote
Okay. Imagine a sound. A simple 'ting' from your phone. Sound travels in waves, you do know what waves look like, right? They're like recurring crests and troughs; up and down respectively. So, for the sake of this example, let's assume that the wave the sound 'ting' makes is one crest and one trough. One up and one down. What noise cancelling earphones do is create the opposite waves of that sound that just entered into them from your environment; which is 'ting' in this case. The earphones will recognize that the wave signature of this sound is one crest and one trough, so what it will do is create one trough and one crest (in that exact order), which are opposites of the 'ting' sound. Then it's going to place this newly created sound over the one that's coming from your phone. When you superimpose both of them together, you get a resultant zero and like that, you end up with noise cancellation.
​
Edit: This explanation may seem a little vague, or I should say 'impractical'. If you're free, have some time, do watch this video to truly see this happening in real time.
GanondalfTheWhite t1_j2dipov wrote
I'm always amazed that it's able to respond so quickly. I'd think the processing time required would introduce more offset than it does.
Implausibilibuddy t1_j2dk2br wrote
It is quick but not instant which is why active noise cancellation works well on low frequencies and not too well for higher.
Low frequency sounds have a wider wavelength (and thus occur over a longer period of time). You can have a little latency between the live and generated sounds and they will still mostly overlap and cancel out. For high frequency sounds there could be several peaks and troughs in the offset gap and they're less likely to line up with the generated sound.
IShouldBeHikingNow t1_j2ewg8x wrote
Which is why they're great an cancelling out the low hum of the airplane but not the shrieking banshee child two seats over?
TheRealAmadeus t1_j2f7f8y wrote
PreCISELY
hgrunt t1_j2ftc1s wrote
It doesn't help that we're particularly sensitive to crying/screaming because it's a sign of distress
frzx1 t1_j2djr04 wrote
There's a lot that goes into noise cancelling, they are not always doing everything in real time. There are specially designed and fully dedicated chips on the sound devices that do just one thing, noise cancelling. They recognize certain sounds and apply the noise cancelling beforehand, thus eliminating that time window. They've been trained on millions of hours of noise and have gotten really good at what they do. Power of data, indeed.
angermouse t1_j2ewgfw wrote
I didn't know noise canceling relied on machine learning. It doesn't need to and the older ones likely did not.
angermouse t1_j2dw1jh wrote
It takes advantage of the fact that light and electrical fields travel about a million times faster than sound (300 million m/s versus 300 m/s). If you think about it, sound is extremely slow. Hearing echoes is a common occurrence and animals like bats even use it for navigation.
noopenusernames t1_j2edsft wrote
It doesn’t have to be perfect to still be effective. Let’s say you have a sound coming in at 150 dB, which is definitely not hearing safe, and the headphones have a delay so they can’t perfectly match up the anti-wave directly over the incoming wave - as long as the anti-wave moves the crests and troughs in the right direction, you create this new wave that’s mostly cancelled out, but you might get some, like 5 or 8 or 3 dB through, which is much safer
The_quest_for_wisdom t1_j2e3wkw wrote
We assume the speed of sound is much faster than it is. Locally it seems almost instantaneous, when it is not.
If you have a large bell like the kind used in a church steeple you can see this disconnect with your own eyes.
If you get more than about an eighth of a mile away you will see the ringing bell move quite a bit out of sync from the sound of the bell ringing that you hear.
It gets even wielder when you consider that the image of the bell being rung is also arriving in your eye AFTER the bell is actually being rung, due to the speed of light. It's just a much shorter delay.
It might be tempting to just hand wave that away and say that the light travels effectively instantaneously, but that thinking with sound is exactly how we ended up here in the first place.
GanondalfTheWhite t1_j2elevv wrote
> thinking with sound is exactly how we ended up here
While everything you said is true, the speed of sound, which, yes, is much slower than light, is still pretty damn fast when we're talking about how much time there is to process something in the time between a soundwave passing from one side of your earbud to the other. Right? Cuz that's what we're talking about. Not how long the sound of something vs. the light of something takes to hit your brain.
Ultimately what we're talking about is that the earbud needs to be able to detect the soundwave, compute its opposite waveform, and emit the counter wave all in the same time that it takes for the soundwave to pass the earbud so that the original wave and the counterwave hit the eardrum at the same time. Right?
So if we assume the earbud is maybe half an inch thick, means it has to do all of that in about 1/27,000th of a second. 0.04 milliseconds.
Even knowing how fast sound travels, that ability to process seems unintuitively quick. That's all I'm saying, it's unintuitive and pretty darn cool.
IsardIceheart t1_j2eb5hh wrote
I'm pretty sure they use pure hardware, no software to do it, because software is too slow.
(This information may be out of date, but this was true not that long ago)
frzx1 t1_j2edyaa wrote
Hardware alone cannot do a lot of stuff that we see today, the true power lies in silicon, and consequently the computation it does. Also, software is far from being 'too slow', I'd even go ahead and say that software at present is far more quicker than hardware.
f4f4f4f4f4f4f4f4 t1_j2ekf2k wrote
Hardware meaning integrated circuits, which are made from silicon...
IsardIceheart t1_j2epxzg wrote
Lmao, yeah this guy is dense.
Also... software is never faster than the hardware it runs on, by definition.
frzx1 t1_j2eknuz wrote
What do you think I'm talking about? CRT monitors?
IsardIceheart t1_j2eg99f wrote
Yeah, okay buddy.
I did some research and it looks like active noise canceling is still done with purely hardware, because software cannot process the sound fast enough.
By purely hardware I mean it is an analog system, not digital.
wbsgrepit t1_j2fc7vq wrote
This is kind of true and kind of false, Software speed is limited by the hardware it runs on — there is certainly software that is fast enough to do this work very well (given the right hardware to run on), however, given the constraints of many noise canceling headphones it is currently much more cost effective to bake that logic into chips especially designed for this work vs using a much more expensive general purpose cpu etc.
IsardIceheart t1_j2fjr4l wrote
Yeah, I guess the point is that general processing is unsuitable for the work, rather than incapable.
JesusLuvsMeYdontU t1_j2dnzjo wrote
So ting comes in and my headphones tang out?
frzx1 t1_j2dol3x wrote
More like,
!!!!! (Goes in)
iiiiii (Comes out)
JesusLuvsMeYdontU t1_j2dp3mr wrote
lol, Eggzaktlee
quarrelsome_napkin t1_j2eb6sl wrote
‘Ting’ goes in, headphones make ‘gniT’ sound at the same time.
AtomicRobots t1_j2fv8y2 wrote
The scientific term for the opposite of “ting” is “gnit”. Ting + gnit = the hollow emptiness of my life these past few months. I need more Ting and less Gnit
chipdipmcgillicuddy t1_j2dj34b wrote
I’ve never used noise cancelling headphones…my question is, do they have a slight white noise to them at all times? That can’t be good for your ears if they do.
frzx1 t1_j2djei4 wrote
In my opinion, bad noise cancelling is worse than no noise cancelling at all. Yes, when the noise cancelling isn't that good and responsive, there are moments of noticeable white noise. But with time, brands have gotten really good at noise cancelling and the manufacturers claiming to have noise cancelling in them do their job well.
chipdipmcgillicuddy t1_j2dksvz wrote
So say you have some good ones, when the headphones hear a noise and play the inverse to cancel it, can you hear that at all? Also, is there a delay? If there was a gunshot far enough away where the headphones could manage to cover the volume of the shot, would it be able to cancel it out in real time? I just don’t understand how sound can be cancelled without some sort of other sound that plays to replace/mask it, in which case it’s not cancelling it just lessening it.
frzx1 t1_j2dlnsp wrote
No, you can not hear it, and that's because it's not being played into your ear, it's being laid on top of the sound that's coming into the audio device. There is no significant delay in it because there are fast dedicated chips in the sound devices that do a lot of computational work when it comes to sound waves. So, they're not always doing this in real time, sometimes they're predicting the sound before it's even completely addressed by the device. If there was a gunshot, far away, yes, it would mask it to a certain degree. That degree is what makes noise cancelling good or bad. There's a lot of other stuff that's done to facilitate the sound cancelling, one of them being plugging the ear completely so that no sound wave enter into the ear directly; no ear cavity is left unsealed. Watch THIS video and you'll be amazed to see how apparent this entire process is.
chipdipmcgillicuddy t1_j2dn3k0 wrote
I thought about it for a few minutes longer and realized this can work because your wearing something right next to your eardrum. Before I was thinking how could sound be cancelled, if I yell at a concert when the band is playing my yell is still there but it’s drowned out, but I guess because the headphones are right next to your ears that must be a big part of why it works.
Techial t1_j2drnu0 wrote
Well, sort of. You also have massive "noise-cancellation" systems built on the same principle when big artists perform live concerts. They literally have subwoofers between the stage and the actual sound-producing subwoofers pointing out to the crowd, and these noise cancelling subwoofers play the same bass sounds (albeit a bit delayed to account for travel) but polarity switched. Imagine sound as a wave going up and down, now if you play the exact same wave but flipped, the waves will cancel out eachother.
nipsen t1_j2dn1d3 wrote
It's a little bit less magical than what people are suggesting here.. You don't actually hear as well, so to speak, as a microphone. So there's enough time to invert the soundwave and play it back before you start picking up the vibrations that produce sound you hear.
Alternative way to think about it - you delay the incoming sound slightly and then play it back as perfectly out of sync as you can. The question really is the response, and how quickly you can generate the wave accurately.
The trick is that you should be producing a sound-wave that sounds like what is actually heard behind the clogs, for example. And you really don't want to play back a really, really loud sound, or increase the wave too quickly based on some extrapolation, etc. And it's typically not perfect, so you get noise. You can also mask it all and increase response, so to speak by having a noise-floor.
But yeah, if you play back some fairly low volume sound where the noise is not physically noticeable, and you allow for some noise on the bottom here -- an exactly out of sync wave is going to cancel the sound out, in the sense that your ear is not going to vibrate and make you hear sound.
WickyNilliams t1_j2dlt8r wrote
I imagine a naive solution would be to add a gate to only cancel noises over a certain db threshold. Also you'd apply some digital signal processing to smooth incoming signal, something like a rolling average or low pass filter to avoid sudden spikes
In my experience the best case for noise cancellation is when there's a constant low level hum eg traffic or airplanes. It works wonders then. I was hesitant about getting a pair but they have been great for me (Sony WF-1000XM4)
IcyMiddle t1_j2dioja wrote
When you're in the bath, you can push the water in one direction to make a wave. A wave has a point where the water is highest, the peak. And a point where the water is lowest, the trough. If you have two waves in the same body of water, they can overlap. When the peaks overlap, you end up with an even bigger peak. But when a peak overlaps with a trough, they cancel each other out.
Active noise cancelling works in the same way, but with sound waves instead of water waves. A microphone picks up the sound you're hearing from outside, and the speakers make the opposite sounds at exactly the right time to cancel them out.
SilentHunter7 t1_j2dji9w wrote
Superposition is a fancy way of saying the whole is equal to the sum of its parts.
If you add two waves, the amplitude of the resulting wave at any point is the sum of both the original waves at the point.
So if wave 1 is sin(x)
And wave 2 is -sin(x)
The two combined give us sin(x) - sin(x) = 0
That's how noise cancelling works.
Note that superposition only works in linear systems. Sound is linear, electromagnetic waves are linear, electric circuits using only linear components (Resistors, Inductors, Capacitors) are linear, etc.
Linearity is definitely beyond an ELI5 discussion though, I think.
CodenameBuckwin t1_j2dngot wrote
Oh my god, that's what that class Linear Algebra was about?! I probably would have taken it if I had any idea about what the heck "linear" was referring to
SilentHunter7 t1_j2dt3ec wrote
Yep! If you remember vectors, Cartesian geometry is also linear. Every vector is a linear superposition of eigenvectors, which are the x,y, and z unit vectors in 3D geometry.
Yeah, mine wasn't that great either. I didn't get it until I had linear signals classes and was like "huh...I wish I paid more attention in my linear algebra class."
They didn't do a very good job of explaining the applications of the class, I feel. Linearity applies to so many things.
fizzlefist t1_j2dumgr wrote
If you insist… HERE I COME TO SAVE THE DAAAAAAAY!
Alterscapes t1_j2ef3r5 wrote
Well, one of them is that you should throw salt over your shoulder if you spill on the table.
55percent_Unicorn t1_j2ed91a wrote
Excellent explanation.
Maybe worth adding that noise cancelling often gets mixed up with noise suppression.
Noise cancelling = actively reducing the noise by making the opposite sound (as described above)
Noise reduction = passively blocking the sound from getting in by plugging/covering your ear canal
FormallyKnownAsKabr t1_j2dkcyn wrote
Also active noise canceling does not block sound and can still cause hearing damage
[deleted] t1_j2dx0qr wrote
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andreipodre t1_j2dydxi wrote
Except you can’t cancel it completely because there is a processing delay to invert the sound waves being played. Because of this delay, instead of getting no sound waves, you get double the amount of waves into your ears. Noise canceling doesn’t prevent ear damage
FormallyKnownAsKabr t1_j2dywa0 wrote
I am aware of annihilation.
I suppose I should have worded differently. ANC will not stop you from getting hearing damage as opposed to something that blocks the sound like ear plugs and the like
UXyes t1_j2dz0a9 wrote
Whelp. I replied to the wrong comment. Lol
FormallyKnownAsKabr t1_j2dz503 wrote
S'all good!
theperfectmuse t1_j2dpc7w wrote
I can't wrap my head around the idea of "opposite sound".
quietcore t1_j2dvfkl wrote
Sound is made up of waves. If you create the opposite wave, the low point of the wave happening at exactly the same time as the high point of the original wave and visa versa then the two waves will cancel each other out.
PokebannedGo t1_j2e4wan wrote
That's because the "opposite sound" doesn't make sense.
If a cat makes a happy meow, the noise canceling headphones does not make a sad meow noise.
The happy meow makes a sound wave
Think of these waves like waves in the ocean
If you were to send the exact same wave from the beach towards the ocean waves, imagine what's going to happen.
Both waves hit together at their peaks and you'll notice that after that point, the waves that would reach dry sand will be much lower in height.
So it's the same wave just coming at the opposite direction
ShouldBeeStudying t1_j2f49sz wrote
If I blare huge sound at my ears it will ruin them. Like gunshots, jet engine or concert speakers. If I blare huge opposite sound at the same time are my ears fine?
Let's ignore the practicality of this please
DragonFireCK t1_j2f6nlx wrote
If you managed a perfect inverse of the wave, the two waves will cancel enough other out and there will be no sound at all. This means that, with perfect noise cancelation, you could be sitting right on top of a jet engine and would hear nothing and have no damage occur.
Practically, getting a perfect inverse is impossible. You'd need a speaker perfectly aligned between the source of the sound and your ears, and the source will actually be a bunch of different points inside the engine, meaning you need roughly an infinite number of infinitely small speakers and microphones.
I did find a video that shows how the phasing works. Its worth noting that the antiphase (opposite) sound will sound the same as the original if heard on its own.
Pixilatedlemon t1_j2f93i3 wrote
It is negative sound
UXyes t1_j2dz486 wrote
Sound waves or vibrations are very small and air is very thin and mostly invisible. It’s easier to understand/imagine using something you can see, like big slow (compared to sound) waves in water.
Next time you’re in a pool or bath or whatever, put your hand flat on top of the water and start moving it up and down in a rhythm to make some sustained waves. Once you’ve got that going, start changing your rhythm and you’ll see that some changes make the waves bigger by amplifying the existing motion or energy in the water, and some changes make the waves smaller by going against the existing wave.
Now think about how there’s a perfect adjustment to that rhythm that will cancel out the existing wave entirely. That’s what’s going on with sound in the air that gets canceled by an “opposite” sound. It’s an opposing wave calibrated just right to cancel the other one.
[deleted] t1_j2epq16 wrote
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femboy_artist t1_j2eprhc wrote
Me either: I get the waves effect, personally, visually it makes sense and by the numbers it makes sense, but I really want to see it in action with sounds because it still doesn’t make sense from a “that’s how it works” perspective.
friendlyfredditor t1_j2f8lf4 wrote
You can do it by playing low noises from two speakers set far apart and walking around between them.
The noise will be louder in some spots and quieter in others.
femboy_artist t1_j2fh9hh wrote
Fascinating. The same sound, I assume? Or different?
bibdrums t1_j2dviqg wrote
Sound travels in waves. The waves travel toward your ears and vibrate your ear drums. Noise cancelling headphones send a wave of the exact shape and speed toward the wave coming at your ear and they crash into each other and the energy from both dissipates.
brazeau t1_j2e3xei wrote
A speaker moves in and out to make pressure waves picked up by your eardrums. You can make a speaker that basically catches the incoming pressure waves.
If one speaker moved outwards, the opposite one would move inward.
Odimorsus t1_j2ecfav wrote
Or the exact (relatively) same sound at exactly the wrong time depending on how you look at it.
GoochyGoochyGoo t1_j2e52za wrote
Those nose bulbs you see on big ships are specifically tuned for each ship and do the same thing with water waves. Lowering friction along the side of the hull and thus improving fuel mileage. As much as 10%.
ThatOneGuy308 t1_j2es2wu wrote
Although, to be honest, most noise canceling headphones are not that exact, so some noise still comes through.
nstickels t1_j2et710 wrote
This is exactly it for “active noice cancelling” headphones. There’s also passive noise cancelling headphones which are far easier in terms of technology and thus far cheaper but they don’t cancel noise as well. Passive noice cancelling just plays a white noise, similar to the sound you hear when you put a seashell to your ear. This noise can help drown out outside noise, particularly when the headphones are also playing something else as well.
Rojibeans t1_j2f09ui wrote
This sounds like some insanely complicated piece of technology. Actually kind of blows my mind
MyOtherAcctsAPorsche t1_j2f7nt1 wrote
Could I stand next to a helicopter with a sufficiently big and well calibrated speaker and not hear a thing? (assuming I have one ear... I guess you can't cancel for two points at a time?)
postorm t1_j2fcdhn wrote
I don't think that is true, or even possible. It does not generate the sound you are about to hear. That would require prescience. It generates the sound that you have just heard, on the assumption that the next sound will be the same. That's why it works well for fairly continuous background noise.
Meenjataka02 t1_j2coo36 wrote
If you imagine sound as an airwave when it picks up sound that it isn’t making it immediately plays an opposite airwave (sound) that cancels out the two sounds in your ear
morold t1_j2d25ep wrote
Does that mean the earbuds use more power in loud environments?
just_push_harder t1_j2d4yql wrote
Never thought about it, but yes, probably.
Sjoerdiestriker t1_j2d60ef wrote
Either that, or the quality of the noise reduction reduces. Imagine again playing a sound with throughs where the original sound had peaks and visa versa, but with a smaller magnitude than the original sound. Now the magnitude of the resulting wave will still be reduced, but not become exactly 0, so the noise cancellation will be imperfect
HolyCloudNinja t1_j2dj3c6 wrote
In particularly hectic environments, my AP Pros struggle to really block a lot of noise, mostly just voices and car sounds, but larger noises still make it through the headphone itself, bypassing the mic (but also hitting the mic, so you get some amount of ANC on it) and hitting your ear.
elsuakned t1_j2evaac wrote
I think this would be a similar question to asking "do my headphones die faster if I listen to things louder", which I don't think is a big enough effect to worry people, I've never heard of it anyways. There's pretty much never not sound. Surely headphones have a lower level of reception or tolerance where it doesn't bother or can't pick up those noises, but it would always need to be listening and ready to generate them, so whether it does and how much it does seems like it'd be the smaller part of the process
Professional-Ad3441 OP t1_j2cp42s wrote
But there must be multiple noises with different wavelengths? Does it consider them as all sounds mixed into one?
BurnOutBrighter6 t1_j2cqp8c wrote
Yes it only considers the combined total mix, not each individual source. All it can do is measure the soundwave that actually reaches your ear, using a built in microphone.
Think of being in a pool. You've got 4 different people swimming, splashing, diving in - making different sizes and types of waves at different locations. But that doesn't really matter - you're at one end of the pool with a little float that bobs up and down and traces the net combined total of all these waves as their combined peaks and troughs reach you.
That little float is like the microphone in noise-cancelling headphones. The microphone measures the total net combined sound wave peaks and troughs reaching your ear, and then the headphones play an "opposite sound" that has peaks where the room noise has throughs and troughs where the room noise has peaks. The peaks and troughs cancel, and the room noise is imperfectly but substantially eliminated.
And yes it's an engineering marvel that this measurement and active response can happen at the speed of sound in an ear-sized device.
constantino675 t1_j2cpfp7 wrote
think of waves in a bathtub or pool, or even an ocean. the waves are highly complex, and you may not be able to cancel them all perfectly, but if you can just knock down the peaks and troughs, you'll make things much smoother.
Throw in some white noise and you can drown out the rest.
brazeau t1_j2e4xxq wrote
It doesn't detect them as multiple frequencies until later, it just samples the incoming sounds and creates a digital version of the analog measurements. from the mic.
There's a thing called 'digital signal processing' which then can then analyze the digital signal and break it up into it's composite frequencies/magnitudes, average out the noise. The way the processing is handled will determine the quality of the end result.
Some cool things to learn about would in Nyquist Theorem, Fast Fourier Analysis, and Digital Signal Processing (FFT is part of this but deserves it's own mention).
ho-tron t1_j2dyt65 wrote
Does it play the opposite sound into the users ear? Or play it towards the incoming sound to ‘shield’ the users ear?
Azi9Intentions t1_j2cqk73 wrote
Imagine a wave of water coming towards you in a wave pool.
Ignore anything to do with things like currents under the water, etc.
If you slap the water as the other wave is coming your way, and make a wave the exact same size, shape, etc, but going the opposite way to the wave that's about to hit you, one stops the other.
Sound in air is much the same, it's just waves that you can't see. The headphones or earbuds with active noise cancellation, simply (or really, not so simply) detect other sounds, and play a sound that is the exact opposite, or close enough.
The waves hit each other, and the sound of both goes away!
hunter_almighty t1_j2ezteh wrote
Just curious, has anyone ever done that with a giant wave pool? I couldn't find any on YouTube, but that would be an awesome visual demonstration
Zosymandias t1_j2fnm15 wrote
There are wave pools where they test scale ships in. You can find demonstrations where they create quilt like patterns using this principle.
Thneed1 t1_j2f5u18 wrote
Not so much an opposite wave going in the opposite direction, but an opposite wave going in the SAME direction.
If the waves are going in the opposite direction, you can’t cancel everything out.
nimitzhunter t1_j2cxrk1 wrote
There are a lot of adults at the pool. Some of them are misbeahving by running clock wise around the pool. The lifeguard got annoyed and send out other adults that run counter clockwise. These adults smash into each others and stop being obnoxious.
Edit: so noise cancelling headphone detects those obnoxious adults, their locations and their behaviors. Then the headphone sends to these location exactly opposite adults and let them smash into each other and cancel each other out.
Edit 2: we can get a bit more technical (eli6 maybe?). The headphone detects the obnoxious adults by running the Fast Fourier Transform algorithm. The algo tells the headphone two things about the obnoxious adults: 1. the adult size (amplitude) and 2. its speed + direction around the pool (phase). The headphone produces the opposite adults with these characteristics: 1. same size (same amplitude) 2. same speed but move in a different direction(antiphase or phase-shifted by 180 degree ie clockwise vs counter clockwise). When the obnoxious adults and the opposite adults smash into each other (destructive interference), they both get knocked the F*** out.
wintersdark t1_j2din5v wrote
Awesome ELI5.
Left__blank t1_j2dosk9 wrote
With the speed of sound traveling so fast, how can it reach the headphone, and the headphone have time to analyze and produce a “matching opposite” so quickly?
pytness t1_j2f6ckg wrote
There is no need to analyze it.
Sound is a wave like this: ---^v---
Notice it goes normal, up, down, normal.
If the microphone gets up, it produces a down and the other way around like this: ---v^---
So if you sum the waves (what u hear) you get --------
Left__blank t1_j2f7tj6 wrote
But it does. You say so yourself: “if the microphone gets up”. Means it picks up the signal and a computer/components must produce an equal and opposite signal to match it and send to your ear simultaneously as that same sound carries into your ear canal. It’s fascinating
pytness t1_j2f90wd wrote
I mean, yeah, but its just -signal
Most speakers go up to 20K hertz, which mean it vibrates up to 20000 a second, if you do the math 1 second / 20000 hertz * 340 (sound speed in meters per sec) = 1.7 mm
Which per each oscilation, sound travels less than 2 mm.
Adversement t1_j2csfkm wrote
The sound you hear is a wave that is a sum of all sounds around you. Waves have a few relevant properties: They travel at a known velocity, and they are additive.
To cancel such wave in your ear: we measure the wave just outside the ear and play its inverse with a small delay from the earphone. Notably, this only cancels the sound in a very small region around the inner side of the earphone. Everywhere else it adds its miniscule amount of more sound to the wave.
For best results: You need a good microphone in both earphones, and a good algorithm to slightly alter the wave, to mimic hiw it will be altered by the earlobe (as the in-ear earphone sound is not altered by the earlobe identically to the sound coming from the outside). Fortunately, we can tune this individually: place a second microphone inside each ear canal (near the very tip of the earphone), and measure which delay and which amplitude modifications reduce the sound the most.
A good analogue: Look at the waves in the see. Measure the height of the wave. If it is above the mean water level, push the water down with a paddle you have placed under the surface. If it is below, push the water up. If you move your paddle at just the right speed for a given measurement, you can destroy the wave around your paddle (whilst creating a new wave around your paddle, propagating outwards and adding a bit to the waves everywhere else in the sea).
patuzzoz t1_j2db6zf wrote
You definitely didn't explain it like I'm 5
Adversement t1_j2dg41h wrote
No, because I read the instructions. ;-) (To explain it with similar complexity as in the question, not to a literal 5-year old. Also, as I expected there to be plenty of literal ELI5 answers.)
plantito101 t1_j2cupft wrote
If it's cancelling the noise, it is it still considered a sound that is received by your ears?
I thought it was a frequency that our ears can't pick up.
DanielEnots t1_j2daq3s wrote
Basically, if you're hearing 1hz sound then once per second the sounds wave goes up and down for a full cycle. To "cancel" it you play a sound that goes down and then up so that you get +1 from outside and -1 front the headphones. And you end up with 0 when you add them.
It's like how I gimbal moves the camera in the opposite direction so even though the person holding it is moving when you add the gimbal movement the camera stays still. There's effectively no sound from outside hitting your ear drum (in a perfect world where it is 100%)
snoopervisor t1_j2dk0hh wrote
Sound is air pressure changes. The canceling means the pressure is flattened. It's substracting two sound waves.
pytness t1_j2f6xm5 wrote
Adding*
nrsys t1_j2d2i22 wrote
Sounds can be drawn as a wave, so for one of the simplest examples let's look at a sine wave - just a simple, regular wave shape.
As a simple maths experiment, if we mirror this wave around the horizontal axis so that where one wave goes up, the other wave goes down, and then add them together, they will cancel each other out.
This works with sound in headphones too. If we stick a little microphone on the outside of your headphones so that it detects the outside sound you will hear, then takes that sound and inverts it so it is upside down and plays that through your headphones, the two will cancel out and the outside sound will vanish. If you play the inverted sound alongside the music or other audio you actually want to hear, you get both at the same time - no outside sound, just the extra audio you are adding.
Incidentally, this works really well with headphones, because the microphone can easily detect exactly what your ear will. If you tried this with a whole room, the way sound reflects off of surfaces will mean that the 'noise' sound will be different depending on exactly where you stand, so it is impossible to cancel it out - you could set it up to cancel nicely in one place, but if you moved about in the room in other places it won't work at all, or may make the noise worse.
[deleted] t1_j2cojft wrote
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5kyl3r t1_j2dfqxk wrote
sounds waves go positive and negative. think of a graph of a sine wave (google it to see a visual). half the time, it's above the line (positive), and half the time it's below the line (negative). that represents the waves moving through the air. that's all sound is. like when you push and pull really quickly on a slinky, you can see the waves ripple down the slinky. sound is like that.
sound waves have what's called a phase. remember the positive and negative thing above? if you reversed the positives and negatives, did you know you still get the same sound? the sound will just be out of phase, but to the person listening, there's no difference. a really really good way to actually hear noise cancelling for yourself is to find a living room setup that has big floor standing speakers. listen to a song with a lot of bass. then on ONE speaker, reverse the wires. meaning connect the + to -, and the - to +. listen to the same song. you'll notice all the bass is nearly gone. that's because waves that have the opposite phase cancel each other out.
think of the times the waves is above the line in the graph as +1. at the point it's crossing the line, it's 0. when it's below the line, it's -1. so one single period, meaning one full section of the wave before it starts repeating over and over, would look like this:
..--.._
or by the numbers we mentioned, like this:
0, +1, 0, -1, 0
now the wave with the opposite phase:
.._..--..
and the numbers for it:
0, -1, 0, +1, 0
now what happens if we add the two waves together?
(0+0), (+1-1), (0+0), (-1+1), (0+0)
0, 0, 0, 0, 0
if we graph that, we just get a flat line. the two waves completely cancel each other out.
in electrical terms, the positive and negative is just voltage, and it's very easy to reverse that with electronics. noise cancelling headphones just have microphones at the edges of your headphones, reverse the wave, and add it to the sound you hear. so if you're listening to music, it'll add the reversed phase wave to your music. you don't hear anything because its values exactly cancel out the original sound. also, this only works because electricity travels nearly at the speed of light, and that's way way way way faster than the speed of sound, so even through the microphone and your ear are only an inch or two apart, it has plenty of time to record, reverse, and add the reversed signal to your audio output. it's really neat stuff
ach_rus t1_j2dguqu wrote
But technically you are hearing 2 opposite sounds? So your hearing membrana in the ear hears both and vibrates and then you interpret it as scilence? Or the waves compensate each other and your ear membrana stays still?
wintersdark t1_j2diief wrote
You don't hear two opposite sounds. The sound waves destructively interfere with each other and no wave remains, thus the membrane in your ear remains still.
ach_rus t1_j2dvjay wrote
Thank you so much for clarification!
zap_p25 t1_j2dhon3 wrote
There are two forms of noise cancellation. Active and passive. Passive essentially means just blocking sounds from getting by such as how over the ear hearing protection works. Active uses electronics and math. The active method is fairly simple to explain though may be more ELI 17 due to geometry and sinusoidal waves. A microphone picks up the ambient noise, and reproduces it in the speaker 180° out of phase which in turn nulls the sum of the noise’s amplitude. The out of phase thing, just means there is an ever so slight delay (which is dependent on the frequency).
MyMomSaysIAmCool t1_j2do65k wrote
There's a third kind that's used for gun hearing protection. Shooters earmuffs use passive noise cancellation, but also have external microphones and internal speakers. When you wear them, the microphones transmit sound to your ears. But they will not transmit any loud noises such as gunshots.
The result is that they give you super sensitive hearing. But there's no risk of hearing damage, because if the electronics fail or the battery goes dead, you're left with passive noise cancellation.
zap_p25 t1_j2dqx8y wrote
Those are a bit different. They don’t use active noise cancellation. They just use the limits of the audio amplification circuitry. Essentially sounds above a certain threshold just don’t get amplified and the passive noise reduction does it’s thing.
MyMomSaysIAmCool t1_j2dxdw8 wrote
That's what I said.
Ganeshadream t1_j2djtj5 wrote
Immagine a still lake. You throw a pebble in the water. Ripple spread out. Then quickly throw another pebble near by. It too makes ripple. Where the first p bibles ripples encountered the second ripples they kinda cancel each other out.
venReddit t1_j2dp7zg wrote
Sound is swinging air. Its like a wave. You have tops and bottoms in the wave. Noise cancelation records the sound and gives back the opposite spike. Top spikes get cancelled with bottom spikes of same strength and other way round. This is why you can feel some sort of pressure in your ears, when you have noise cancellation in your ears without actual music, when the outside is loud.
angrybird7677 t1_j2du3zj wrote
It's wizardry dark magic that technology can "predict" outside noises and create the opposite sound in real time. There's no other way to explain this!
adamtheskill t1_j2e4nxy wrote
The idea is somewhat simple, you simply measure (and in more expensive/sophisticated headphones predict) the noise coming into the ear and use that info to send noise into the ear which exactly counteracts the incoming noise you want to block.
There are several insanely difficult parts to this though:
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How do we calculate what we need to counteract incoming noise fast enough that we actually counteract it in time? In airpods there may be a couple centimeters between the outer speakers measuring incoming noise and the inner speakers. This gives distance/speed of sound ≈ 3*10^(-2)/343 ≈ 1/10000 seconds, so 100 microseconds. That's not a lot of time to calculate things.
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The noise being measured at the outer speakers is distorted due to the shape of your ear. This needs to be taken into account or otherwise the inner speakers would not be cancelling out the correct sound.
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Predicting what noise will be coming and using the prediction instead of actually measuring the noise. This works pretty well for a lot of signal processing purposes (separating noise from music, recreating ECG's when only part of the data is available, or anything else where the input can be considered a signal) but real life noise is not always predictable.
[deleted] t1_j2e8z9k wrote
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outofmemory01 t1_j2egssu wrote
A speaker works by shoving air forward...active noise cancellation works by sucking in the diaphragm at the same moment the 'force' of outward air to 'suck in' the energy. Microphones and knowing the speed that sound travels is what allows the noise cancellation circuitry to know exactly when to provide that 'hollow' space to cancel the noise.
No noise cancelling headphone cancels deeper frequencies as well as higher ones...the bigger the diaphragm the lower the frequency you can 'catch'. Most noise cancelling starts with passive noise cancelling - which is a fancy word for 'plugging your ears' - ala foam/vinyl/leather to block the sound from getting in. In smaller air buds you're automatically getting passive noise cancelling just by shoving them in your ears. Also your ears can only 'hear' the most powerful push...your eardrum is a diaphragm too. But it can only 'hear' the loudest thing at any given time. Many active headphones just produce a white noise 'hiss' which is amazingly effective at just drowning out the randomness of noise...and your brain just loves it as it only takes a few minutes for your brain to stop hearing that hiss/hizz noise.
Edit: Consider stereo systems...the bigger the speaker the deeper the bass. No one has 'tweeters' thumping the bass. And in ear phones have tricks to increase the bass - but the bigger the driver the better the bass sound you can get.
Euphorix126 t1_j2ehqeu wrote
In two words: destructive interference.
If you and a friend hold a rope taut, and your friend raises and lowers their hand once very quickly, a wave will travel on 'top' of the rope to you. If you move your hand down and up quickly, a wave will travel along the 'bottom' of the rope toward your friend. If you and your friend did this at the same time, when the two waves meet in the middle, the rope will be completely flat for an instant.
[deleted] t1_j2er24f wrote
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fatman06 t1_j2etvqq wrote
I had the same question a few years ago, this video did a great simple explanation that helped me understand what's going on
daveonhols t1_j2fg678 wrote
I was told in university that noise cancelling headphones used by jet pilots work by subtracting white noise from the sound they are playing, in the belief that generic "outside noise" was something like white noise (probably not a bad approximation when you are next to a jet engine), and subtracting it has the effect of cancelling it out. This was in the days before noise cancelling was a feature of consumer headphones, but I always assumed the principle was the same.
stevey83 t1_j2d8i8t wrote
Does it affect the quality of the sound your hearing?
wintersdark t1_j2dic0k wrote
Not really, no. You're cancelling our outside noise, but the sound made by the speakers inside is largely unaffected.
In practice, the cancellation is imperfect (that is, you can't use ANC to obtain total silence) so remaining outside sound will impact resultant listening quality...
But that's the case without ANC too, and it's worse then.
[deleted] t1_j2cor0w wrote
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Professional-Ad3441 OP t1_j2cp7y4 wrote
watching porn Why is everyone staring at me
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Sparquee t1_j2coklw wrote
The speaker sends out a tone at a very high frequency. That frequency is particular that it actually interrupts noise outside. Think of if you run your ear aggressively as if you're itchy, you might get a high eering tone afterwards. You may also have noticed you don't hear anything for a few seconds. That's the whole concept of noise cancellation.
Hope this helps.
jswansong t1_j2csto6 wrote
You know how your headphones can reproduce any sound? Noise cancelling headphones have microphones to detect what outside sounds you're about to hear and then make the exact opposite sound at exactly the right time. Any sound (no matter how complex or loud) + its exact opposite = no sound at all, much like 5 + (-5) = 0.
I could get into superposition and all that, but that's probably beyond age 5.