4 ms·

The reason noise cancelling headphones work is that, by being out of phase, the two sound sources sum to zero (or closer to it). It's not just a trick of the br

The reason noise cancelling headphones work is that, by being out of phase, the two sound sources sum to zero (or closer to it). It's not just a trick of the brain making you ignore the sound because an out of pass signal is also present. The out of phase signal causes the actual sound pressure level to decrease by cancellation. So yes, there is less sound pressure.

afandian 8y ago
The fact that noise cancelling headphones cause me pain made me question that. I wonder if the wave interference does indeed sum to zero, or to a constant DC offset. Obviously there's no such thing as a constant pressure in acoustics, but something's happening...
- Traubenfuchs 8y ago
  Have you tried ear plugs? You can even combine them with headphones for ultimate cancelling.
  - afandian 8y ago
    I have a pair in my pocket now!
  - mlthoughts2018 8y ago
    In two separate jobs, I had managers tell me it was “rude” for me to wear ear plugs, even after I explained to them that the office noise was unbearable and noise-cancelling headphones are painful for me to use. It’s 100% about virtue signalling to management. Headphones fit the visual stereotype of a hacker, so it’s OK. Ear plugs carry a connotation that the stuff generating noise is somehow “a bother” or “a nuisance” ... which of course is true, but you’re not allowed to actually acknowledge that truth.
    - ryandrake 8y ago
      Just get an old pair of headphones that don’t work and put them on over your ear plugs.
      - mlthoughts2018 8y ago
        The physical feeling of wearing over-the-ear headphones, ear muffs, etc., is extremely uncomfortable for me. Even with very expensive “ergonomic” headphones, I can’t stand the feeling for more than a few minutes. When I’m actually listening to music, only earbuds will work for me. I suppose I could try to get earplugs that look like decoy earbuds. However, if your comment was meant seriously, i.e. that employees should do some noise-cancellation arms race song and dance with employers, that mildly terrifies me. How could any person actually think that it’s acceptable to let your employer treat you that way? It’s insane. The actual best option is to first do excellent work that makes your employer respect you and really count on you to such a degree that firing you for expressing reasonable preferences is not realistic for them. Then once you have established that bar of credibility, find the right ways to constantly remind your manager and other managers that the workplace conditions are unacceptable. This requires political tact because outright grumbling or long-winded feedback sessions will be used against you. Rather instead, you have to find key moments to unassailably undermine your boss by visually demonstrating just how hard you’re working but keep pointing out that because of noise and distractions, nobody (not even good, old trustworthy you) can get the thing done on time or get the full set of features implemented, etc. You have to convert your pain into your boss’s boss’s pain, or it will never change. Capitulating with headphone contortions is a terrible approach.
        ryandrake 8y ago
        I agree with what you said in principle but I was going for a practical solution rather than an ideal one.
        mlthoughts2018 8y ago
        So was I. Above all else, capitulating to change the debate into a question of which type of headphones to wear is not practical, because it doesn’t address the underlying negative health effects. To qualify as “practical” an idea would first have to at least meet the criteria of alleviating the physical disergonomy of the situation, or at least contribute to that over the long term. Anything which proposes to just “put up with it” in some way or another would be as impractical as possible, because not putting up with it is the sole property required for anything to count as a productive approach.
    - jonhendry18 8y ago
      That's funny. Plenty of "real jobs" like welding require ear plugs.
      - mlthoughts2018 8y ago
        If the ear plugs are for a “real” reason, like safety or even required OSHA regulations, then of course the workplace culture around it develops to lend it credibility. But in tech companies it’s all about optics.
  - Afton 8y ago
    Earplugs and brown noise. I can just, if I concentrate, make out _that there are people talking_. But since I completely can't parse it, it doesn't disturb me. The earplugs mean that I can listen to it at a much greater volume that would be comfortable/safe without them. The downside is that every time someone wants to actually talk to me, I have to take my headphones off and take at least one earplug out.
- mike_ivanov 8y ago
  Most likely it's high-frequency (ultrasound) noise cancellation artifacts that you don't exactly hear, but they might manifest in what you experience as pain.
- jdbernard 8y ago
  It is possible that the cancellation is not perfect and there are still pressure waves hitting your ear at frequencies outside the range of human hearing. Or it's also possible that just having the cans over your ears is causing fatigue, separate from any actual sound pressure. As far as a DC offset, that doesn't exist in actual sound pressure waves. That's an artifact of discrete representation of sound as an electrical signal. When a DC offset is connected to a speaker you don't actually get any sound pressure, because the sound pressure comes from the cone's movement pushing air (resulting in pressure waves in air). A DC offset just means that the speaker is being held still at some offset from it's "zero" or resting position. But the speaker is still being held still, un-moving, so no pressure waves are created. The "pop" you sometimes hear when a DC offset is present is the transition from a neutral signal (no offset) to the DC offset. The immediate change in the signal causes the speaker to move as fast as physically possible to get to the new position, creating a short, often very strong pressure wave (the pop). But once the speaker is at the offset it doesn't move unless the signal changes. As you say, there is no "constant pressure" in acoustics. Or more accurately, it's typically not a factor in sound reproduction. Technically we are all subject to the constant atmospheric pressure. But it's not the pressure that causes acoustic phenomena, it's the rapid fluctuations in pressure. It's even possible that the headphones are forming a seal around your ear and subjecting your ear to varying pressures as you move and the headphones shift on your head (too slowly to be perceived as sound).
- wilsonnb2 8y ago
  You should differentiate between active noise cancelling and passive noise cancelling. Active noise cancelling is what fancy Bose and Sony and (simply put) it involves cancelling outside sound out by playing the opposite sound. This shouldn't cause hearing damage because the opposite sound waves actually sum to 0, but I'm unaware of any studies about this so who knows. Passive noise cancelling is when your headphones block out outside sounds the same way that typical ear protection does - by physically preventing it from getting inside the ears. Most headphones (excluding open-back headphones) will have some degree of passive noise cancelling just because they need to cover your ear. You can buy headphones designed to passively block as much noise as possible. They are typically called IEMs (in ear monitors) because they are commonly used by musicians on stage to hear their instruments and what not. This kind of noise cancelling will absolutely not damage your hearing or cause pain. In fact, because of the lower ambient noise while listening, you will be able to listen at lower levels. That will cause even less hearing loss and pain. I've got a pair of these [1] Etymotic IEM's. I also use Etymotic's musicians earplugs and the IEM's block out pretty much the same amount of sound and fit in the ear the exact same way. Other notable brands are Shure and Westone. If you want, you can go the extra mile and have custom molds made of your ears. Those will be far more comfortable than universal IEM's and will block more noise, too. [1] https://www.amazon.com/Etymotic-Research-Noise-Isolating-Ear-Earphones/dp/B003S3RFIQ/ref=sr_1_2?ie=UTF8&qid=1530644361&sr=8-2&keywords=etymotic+iem https://www.amazon.com/Etymotic-Research-Noise-Isolating-Ear...

afandian 8y ago

The fact that noise cancelling headphones cause me pain made me question that. I wonder if the wave interference does indeed sum to zero, or to a constant DC offset. Obviously there's no such thing as a constant pressure in acoustics, but something's happening...

Traubenfuchs 8y ago
Have you tried ear plugs? You can even combine them with headphones for ultimate cancelling.
- afandian 8y ago
  I have a pair in my pocket now!
- mlthoughts2018 8y ago
  In two separate jobs, I had managers tell me it was “rude” for me to wear ear plugs, even after I explained to them that the office noise was unbearable and noise-cancelling headphones are painful for me to use. It’s 100% about virtue signalling to management. Headphones fit the visual stereotype of a hacker, so it’s OK. Ear plugs carry a connotation that the stuff generating noise is somehow “a bother” or “a nuisance” ... which of course is true, but you’re not allowed to actually acknowledge that truth.
  - ryandrake 8y ago
    Just get an old pair of headphones that don’t work and put them on over your ear plugs.
    - mlthoughts2018 8y ago
      The physical feeling of wearing over-the-ear headphones, ear muffs, etc., is extremely uncomfortable for me. Even with very expensive “ergonomic” headphones, I can’t stand the feeling for more than a few minutes. When I’m actually listening to music, only earbuds will work for me. I suppose I could try to get earplugs that look like decoy earbuds. However, if your comment was meant seriously, i.e. that employees should do some noise-cancellation arms race song and dance with employers, that mildly terrifies me. How could any person actually think that it’s acceptable to let your employer treat you that way? It’s insane. The actual best option is to first do excellent work that makes your employer respect you and really count on you to such a degree that firing you for expressing reasonable preferences is not realistic for them. Then once you have established that bar of credibility, find the right ways to constantly remind your manager and other managers that the workplace conditions are unacceptable. This requires political tact because outright grumbling or long-winded feedback sessions will be used against you. Rather instead, you have to find key moments to unassailably undermine your boss by visually demonstrating just how hard you’re working but keep pointing out that because of noise and distractions, nobody (not even good, old trustworthy you) can get the thing done on time or get the full set of features implemented, etc. You have to convert your pain into your boss’s boss’s pain, or it will never change. Capitulating with headphone contortions is a terrible approach.
      - ryandrake 8y ago
        I agree with what you said in principle but I was going for a practical solution rather than an ideal one.
        mlthoughts2018 8y ago
        So was I. Above all else, capitulating to change the debate into a question of which type of headphones to wear is not practical, because it doesn’t address the underlying negative health effects. To qualify as “practical” an idea would first have to at least meet the criteria of alleviating the physical disergonomy of the situation, or at least contribute to that over the long term. Anything which proposes to just “put up with it” in some way or another would be as impractical as possible, because not putting up with it is the sole property required for anything to count as a productive approach.
  - jonhendry18 8y ago
    That's funny. Plenty of "real jobs" like welding require ear plugs.
    - mlthoughts2018 8y ago
      If the ear plugs are for a “real” reason, like safety or even required OSHA regulations, then of course the workplace culture around it develops to lend it credibility. But in tech companies it’s all about optics.
- Afton 8y ago
  Earplugs and brown noise. I can just, if I concentrate, make out _that there are people talking_. But since I completely can't parse it, it doesn't disturb me. The earplugs mean that I can listen to it at a much greater volume that would be comfortable/safe without them. The downside is that every time someone wants to actually talk to me, I have to take my headphones off and take at least one earplug out.
mike_ivanov 8y ago
Most likely it's high-frequency (ultrasound) noise cancellation artifacts that you don't exactly hear, but they might manifest in what you experience as pain.
jdbernard 8y ago
It is possible that the cancellation is not perfect and there are still pressure waves hitting your ear at frequencies outside the range of human hearing. Or it's also possible that just having the cans over your ears is causing fatigue, separate from any actual sound pressure. As far as a DC offset, that doesn't exist in actual sound pressure waves. That's an artifact of discrete representation of sound as an electrical signal. When a DC offset is connected to a speaker you don't actually get any sound pressure, because the sound pressure comes from the cone's movement pushing air (resulting in pressure waves in air). A DC offset just means that the speaker is being held still at some offset from it's "zero" or resting position. But the speaker is still being held still, un-moving, so no pressure waves are created. The "pop" you sometimes hear when a DC offset is present is the transition from a neutral signal (no offset) to the DC offset. The immediate change in the signal causes the speaker to move as fast as physically possible to get to the new position, creating a short, often very strong pressure wave (the pop). But once the speaker is at the offset it doesn't move unless the signal changes. As you say, there is no "constant pressure" in acoustics. Or more accurately, it's typically not a factor in sound reproduction. Technically we are all subject to the constant atmospheric pressure. But it's not the pressure that causes acoustic phenomena, it's the rapid fluctuations in pressure. It's even possible that the headphones are forming a seal around your ear and subjecting your ear to varying pressures as you move and the headphones shift on your head (too slowly to be perceived as sound).
wilsonnb2 8y ago
You should differentiate between active noise cancelling and passive noise cancelling. Active noise cancelling is what fancy Bose and Sony and (simply put) it involves cancelling outside sound out by playing the opposite sound. This shouldn't cause hearing damage because the opposite sound waves actually sum to 0, but I'm unaware of any studies about this so who knows. Passive noise cancelling is when your headphones block out outside sounds the same way that typical ear protection does - by physically preventing it from getting inside the ears. Most headphones (excluding open-back headphones) will have some degree of passive noise cancelling just because they need to cover your ear. You can buy headphones designed to passively block as much noise as possible. They are typically called IEMs (in ear monitors) because they are commonly used by musicians on stage to hear their instruments and what not. This kind of noise cancelling will absolutely not damage your hearing or cause pain. In fact, because of the lower ambient noise while listening, you will be able to listen at lower levels. That will cause even less hearing loss and pain. I've got a pair of these [1] Etymotic IEM's. I also use Etymotic's musicians earplugs and the IEM's block out pretty much the same amount of sound and fit in the ear the exact same way. Other notable brands are Shure and Westone. If you want, you can go the extra mile and have custom molds made of your ears. Those will be far more comfortable than universal IEM's and will block more noise, too. [1] https://www.amazon.com/Etymotic-Research-Noise-Isolating-Ear-Earphones/dp/B003S3RFIQ/ref=sr_1_2?ie=UTF8&qid=1530644361&sr=8-2&keywords=etymotic+iem https://www.amazon.com/Etymotic-Research-Noise-Isolating-Ear...