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EMF generator from audio speaker

  1. Aug 9, 2014 #1
    Hello everybody, I am trying to figure out how to build an electro magnetic generator.
    I was wondering if an audio transducer such a speaker could act as a EMF generator, when the paper woofer is removed and the device connected to a function generator and an amplifier, in order to play the signal with the magnet only.
    Would it be the same thing?
  2. jcsd
  3. Aug 9, 2014 #2


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    You already have a function generator and an amplifier, so you can generate an AC EMF using these.
  4. Aug 10, 2014 #3


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    The windings in a speaker voice coil will generate a magnetic field, same as any coil. The speaker coil is suspended near a permanant magnet, so it can move when the fields of the coil and magnet interact.
  5. Aug 10, 2014 #4

    jim hardy

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    That's a statement not a question.
    A question well stated is half answered.
    What is the question ? I got frustrated tying to figure that out.

    sure, you can use one for a microphone.
    A speaker is one form of electric motor, it makes electrical energy into motion using magnetic principles.
    that i understood, if you meant the paper 'cone'.

    What device? The voice coil or the speaker suspension?

    Connected how? Mechanically by perhaps a spot of glue to dust cover, or electrically by wiring to the terminals?

    An electronic one to force current through the voice coil?
    Or a mechanical camshaft based one that'll physically move the suspension and coil back and forth?

    To the amplifier's input or to its output?

    play = to reproduce it? As mechanical motion or as electrical voltage?

    The magnet isn't going to play anything.

    Please put some more thought into phrasing your question.
    Then state it as a question, and the friendly folks here will try to help you figure it out.
  6. Aug 10, 2014 #5

    jim hardy

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    Since you're into Schumann waves, why not build something to measure them ?
  7. Aug 11, 2014 #6


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    Lol :rofl:
  8. Aug 11, 2014 #7
    My plan is to reproduce a waveform thru a software, the audio output will go out of the soundcard to the input of a tripath audio amplifier, in order to be reproduced by a coneless speaker using banana plugs. I was wondering if a speaker voice coil would generate a magnetic field same as any coil ?

    This answers my question. Thank you! :thumbs::smile:

    As I am interested in measuring the effectiveness of a magnetic field on the brain I think I might need an EEG to collect data, and it seems like a DIY solution could cost more than an actual second hand device.

    A normal coil picking up signals from the scalp would be too weak, and loads of filtering needed because of many muscles in the face area.

    It's a bit of a grey area with contrasting experiences..hence why I'd love to do some experiment.

    Only publication I've found it's over here about the 'God's Helmet' http://www.ncbi.nlm.nih.gov/pubmed/15849873

    I didn't mean to get people frustrated with my lack of technical language, thank you for your patience and inspiration! :smile:
  9. Aug 11, 2014 #8


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    A loudspeaker coil is not what you want if you want to produce varying magnetic fields. A voice coil is made specifically to operate in a strong magnetic field and uses the motor effect. It has a very few turns and is light enough for it vibrate and move the cone. You do not want this; you need to produce a decent field from your coil. You will need many turns of wire for this. When you have found out the sort of field you will need then you can start to specify the required system. Approaching this with random stuff, connected together, will not achieve anything but wasted time.
    People are not frustrated by your lack of technical knowledge. They are frustrated because you are not asking answerable questions. In your last post you seem to be confusing the production and detection of magnetic fields. What is it you want to do, exactly?
    Last edited: Aug 11, 2014
  10. Aug 11, 2014 #9

    jim hardy

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    A friend of mine built one for high school science fair circa 1963, vacuum tube of course. It's a wonder we didn't hurt ourselves. He sensed signals on surface of scalp. At those low frequencies it takes a lot of flux to make voltage that's measureable with a reasonable sized sense coil so he went to direct contact. Besides, he thought brain waves express themselves as a voltage phenomenon not a magnetic one.
    With today's micropower devices it'd be a lot more feasible.

    That's the spirit. Ability to take criticism with grace indicates you're a man of distinction (to quote Peggy Lee.) Thanks in kind.

    Yes you seem to be mixing concepts. That's what confused me, "Does he want to make a magnetic field or does he want to make voltage by moving a coil inside one?"
    Your speaker idea is great for the latter but not i fear the former.

    If you want to expose a brain to low frequency magnetic fields it seems to me you need to both create and measure such fields. Else you wont know what field you've made or what is background field from earth.

    I suggest you study up on basics of magnetism

    Earth has an electric field, too ...............
    Last edited: Aug 11, 2014
  11. Aug 11, 2014 #10


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    Your previous thread on this topic was locked for a good reason:


    This thread is closed as well. Check your PMs -- do not post about this again here.
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