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I know it has to do with electricity flowing and generating a magnetic field, but I would like a thorough explanation (with perhaps a picture). In particular:

  • What is in the ear piece?
  • Why do they repel as opposed to attract?
  • How come my ear buds don't seem to do it?

Thanks in advance!

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Nice question! Observation: my earphones do it also when they're not plugged in. So either there is some magnet inside or there is some residual magnetization left from earlier. –  Marek Nov 26 '10 at 16:41
    
Yes, mine do too actually. I believe there is a magnet in there -- but the effect is drastically magnified when the music is on :-). –  Tom Nov 26 '10 at 16:50
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On a related note: see my question on meta.physics about how to tag this questions: meta.physics.stackexchange.com/questions/170/… –  Tom Nov 26 '10 at 16:51
    
My daughter's earbuds magnetize TOGETHER, not opposing and they shocked her once. Anyone know why? –  Donna Dec 28 '10 at 2:51
    
Hi, Donna. I see you're new, so welcome! While I do not know the answer to this, I would encourage you to post a separate question rather than an answer to this question because you will risk getting downvotes :-). You can just post a link to my question in your question so people can read it as background. I suspect people will just say that the way the earphones are designed, the magnets happen to orient themselves in a way that they attract. And the shocking is (probably?) unrelated to the magnetism and could have been caused by something else. –  Tom Dec 28 '10 at 3:05

2 Answers 2

What is in the ear piece?

Normally there is a small magnet, a loop of coil and a diaphragm. The current going through the coil is modulated so that it makes the coil move in the magnetic field and the diaphragm, which is attached to it. The movement of the diaphragm generates the sound.

Why do they repel as opposed to attract?

Because the two magnets are oriented the same way.

A longer and more interesting answer is the following. Most modern music has monaural lower frequencies. This is because the kick drum and the bass in rock and pop are positioned in the centre of the audio spectrum.

Now, the lower frequencies are the ones that need more electromagnetic energy, because they need to push more air - the wavelength is longer - and they are in-phase between the two ear pieces.

So in practice, when you listen to music, you feel more force pushing outwards. If you were to listen to music with out of phase basses, you would feel less force.

How come my ear buds don't seem to do it?

For a number of reasons.

  • they are smaller, therefore there are smaller forces involved
  • the diaphragms are smaller and the earbuds are therefore built to have far less low frequency response
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Nicely explained. –  Greg Nov 26 '10 at 22:47
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The current is not "frequency modulated". Faraday shields don't have any effect on low-frequency magnetic fields. You need mu-metal for that. –  endolith Nov 28 '10 at 15:40
    
The reason the two magnets are oriented the same way is because it's cheaper to make both sides identical. It's possible for them to be mirror images, with magnets and coils flipped, but it would make no economical sense to do so. –  endolith Aug 15 '11 at 3:24

Because the loudspeakers in your earphones (or at least @Marek's) contain some permanent magnets. To make a long story short, the magnetic field produced by the current is used to move the permanent magnet according to the music you're hearing. Then, the details depend on the specific technology your earphones use, as you can check with http://en.wikipedia.org/wiki/Earphone#Technology (with diagrams)

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"...so, in effect, the earphone becomes an electromagnet." –  Mark C Nov 26 '10 at 18:57

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