I <3 Katy Perry









Man I LOVE that song!  I could just sing it all day long! On the train, on a plane, right beside you, in your ear-hole.

Supposin’ you don’t like the power-pop that my girl Katy likes to sing?  Well then you’ve got two choices: 1) Challenge me to a sing-off.  2) Put on some noise-canceling headphones.

Trust me, you don’t want to challenge me to a sing-off.

So you’ve chosen to put on some noise-canceling headphones? Wise choice…

But how do they work?  Don’t they have something to do with magnets?

Well, yes… most forms of speaker use magnets to… never mind, I dont talk to Juggalows.

I digress… “Noise Canceling” headphones are really just regular ol’ headphones with two small differences…

Regular headphones receive a signal from your iPod, CD player, 8-track, etc… and convert that signal into the vibration of a diaphragm, which creates noise which you interpret as bad music….  (No offense to your music tastes, but it’s just so cliche to have a favorite band that no one’s ever heard of… Katy Perry is all you need.)

Noise canceling headphones do the same, except that they also listen to the environment around you, and attempt to “cancel out” any noise that you might be hearing that isn’t from your desired audio source.  In theory, this means you could be sitting on an airplane in flight, and not be able to hear the drone of the engines, or the whine of the baby down the aisle.

In reality though, they aren’t able to completely cancel ALL the noise around you.  Even the super-high-end noise canceling headphones can only “cancel out” a certain percentage of the outside noise.  There are a lot of complicated reasons for this, so I won’t go into them here, but suffice it to say…they ain’t perfect.

So a more accurate name for noise canceling headphones might be an “Active Noise Attenuator”.  This is opposed to a “Passive Noise Attenuator”, which would simply be earplugs.  In reality, if silence is what you want, earplugs are going to do much better than most noise canceling headphones.

Hang them from your car mirror to blend in with construction workers

Noise Canceling headphones operate on the Superposition Principle of wave mechanics.  The idea is that when two waves encounter each other, they will “superimpose” their characteristics upon one another, creating a new wave that is a combination of the two original.  The figure below shows the two extremes of superposition; 1) If the two waves are “in-phase” they add together, creating a larger amplitude wave, and 2) If the two waves are “out-of-phase” they subtract from one another, completely eradicating both original waves.

(FYI: This applies to particle/pressure waves like water and sound, as well as electromagnetic waves like light)

Your noise canceling headphones are using this concept to attempt to “cancel out” the sound waves from the outside environment via two simple components: 1) a microphone to listen to the outside noise, and 2) a small signal processor to create the waveforms necessary to cancel the outside noise.

That’s it.  No fancy, super computer living inside your headphones… no complicated materials or wiring.  Just a little microphone and a processor less sophisticated than the one in your 5$ Timex watch.  So why are they so expensive?

399$ !?!?!?!? That better be for the headphones AND the girl!

Simple. They’re expensive because they sound expensive.  “Noise Canceling” sounds really fancy, because most people don’t understand how it works, but in reality it’s just adding a little bit of extra noise to your headphones, which through some physics magic, results in reducing the perceived volume of the outside noise.

Are they a good idea? Certainly.

Are they worth it? Not at all.  Earplugs can literally be bought with the change in your pocket, and do a much better job of creating silence for your ear-holes.

Maybe one day  some company will figure out how stupid this is and starts selling noise-canceling headphones for 2$ more than regular headphones, then they’ll be worth it, but for now just listen to Katy Perry, sing really loud, and I’m sure you won’t be able to hear anything else for WEEKS.

Bonus: Although this technology is a sham for headphones, it’s being tested on a larger, 3-dimensional scale to reduce the noise of aircraft in communities near airports! Loudspeakers are set up around the airport that play the off-phase sound waves for the engine noises, and word-on-the-aerospace-street is that, after a lot of optimization, it works really well!




  1. JoshuaNo Gravatar 13 July, 2010 at 9:43 am #

    Actually, speaking of earplugs, the latest thing for earbud headphone design seems to be silicone earplugs with holes to admit sound from the headphone speakers. They work really well, and the darn things only cost $20-30 for the top-of-the-line brands. You can even get earbuds that have memory foam earpieces that fit the shape of your ear canal exactly to block out external sounds. Which is a bit weird, but I’m sure very effective.

    • JacobNo Gravatar 13 July, 2010 at 9:55 am #

      Very True!

      My fiancee can’t stand those kind of earplugs, and I can’t wear them at work because I need to hear when someone sneaks up on me, but I have worn them on an airplane before and they worked pretty well!

      Thanks for the comment, Joshua!

  2. benNo Gravatar 13 July, 2010 at 4:58 pm #

    what happens if someone challenges you to a singing contest?

    • JacobNo Gravatar 14 July, 2010 at 4:18 am #

      Just ask Simon Cowell…

  3. dkNo Gravatar 30 August, 2010 at 12:22 pm #

    You get stuck hosting American Idol and look completely pissed off for life?! You are one bad assed sing-off competitor, sir!

    I’ve been using the Shure passive noise-cancelling headphones for years, and love them. However, like you, I can’t wear them at work, which is when plain old iPod buds work great…they leak so much sound you can hear everything around you, as well as your Amon Amarth (swedish Viking metal…far more mainstream than ms. perry, no? NO?!?)

  4. dkNo Gravatar 31 August, 2010 at 10:38 am #

    Follow-up question, though this might be more bio-medical in nature:

    If there was a deafening sound source, what would happen if you had a speaker cancelling it? Would it still register as silent at the ears, or would there still be danger involved (ignoring the realities of moving out of the sweet spot and suddenly having two extremely loud sound sources.) This was inspired by the idea of having cancellation speakers around airports. Living a stone’s throw from JFK, that sounds lovely, but I can’t make the physics work: wouldn’t that need speakers every few feet to account for distance and phase, as well as listener location?

    • JacobNo Gravatar 1 September, 2010 at 6:38 am #

      Very good question.

      If you assume that we can achieve PERFECT sound cancellation (which we can’t), then you can think of it like this:

      – imagine the incoming sound as a billiards ball rolling in from the right side of your screen
      – imagine the “canceling” sound as a billiards ball rolling in from the left side of your screen

      Both balls are the same mass, and are rolling at the same speed. So when they strike (perfectly aligned) in the center, they both stop moving.

      Since sound energy is just the kinetic movement of air (caused by pressure differentials), if an equal and opposite movement of air encounters the incoming sound, the kinetic energy of each source is completely canceled by the other.

      SO, back to your question. If there were an incoming deafening sound source from 100 feet away, the “canceling speaker” would need to produce an equally deafening sound, in opposite phase, in order to cancel it out. So you would need to place your “canceling speaker” in between you and the source, otherwise you’d be deafened by the canceling speaker just as easily.

      The idea of using them in airports isn’t far-fetched, and I had a professor tell me that it’s already being tested, although since then, i havent heard anything else about it.

      And yes, due to the spherical propagation of sound waves, you would need a lot of speakers around an airport in order to make it work. Probably not every few feet, but enough so that the variation in cancellation is minimized. It’s probably POSSIBLE, but like I mentioned in the blog, it’s extremely complicated when you get into 3-dimensional space, which might make it too cost-prohibitive to justify.

  5. dkNo Gravatar 1 September, 2010 at 11:22 am #

    Thanks for the answer…much as I suspected, but nice to see I’m not completely off in left field. Just followed your link in the post to the ICP/Magnets thing. Not sure how I missed out on that meme, but it is pretty awesome. ;)


  1. We played with lasers. – xthephysicist - 21 February, 2016

    […] – for the pic of superposition of waves […]

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