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Motionless speaker

  1. Oct 16, 2006 #1


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    i thought of a design of a motionless speaker,
    it consisted of a LARGE electromanget that when charged, would attract atoms in the air toward the magnet. then immediatly after that, change the polarity of the magnet and therefore repelling the atoms. repeating this motion would creat pressure waves in the air. all sound is is a fast variance of pressure.
    i wanted to be sure that this is only impossible because the "air" consists of ~75% nitrogen. if you look it up, nitrogen has no charge. therefore making my idea imossible:grumpy: . unless the remaining 25% that is possibly charged would work. i know that when you change the polarity of an electromanget very quickly, you dont hear anything. WHY DONT YOU HEAR ANYTHING?!?!:surprised i dont understand why this woulden't work dispite the massive ammount of nitrogen (-) as described in this diagram:
    pardon my spelling and grammar.

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  3. Oct 17, 2006 #2
    Air is generally electrically neutral.
  4. Oct 17, 2006 #3
    As is water, but you can demonstrate in your sink the attraction of water to an electrostatically charged rod. Is the induced dipole moment what causes high voltage lines to hum?
  5. Oct 17, 2006 #4

    You don't hear anything, because, as the above poster stated, air is chargeless....however, you could possibly charge the air in the region somehow.

    And also, electromagnets, or any magnet for that matter, doesn't attract or repel charge....magnetic fields exert forces on MOVING charges....not simply charges. ELECTRIC fields exert forces on stationary and moving charges....an electric field can be produced by a charged plate, for instance. You could charge air near the plate somehow and then charge the plate. If you rapidly alternated the sign of the charge on the plate you could get the air near the plate to vibrate thus producing a pressure wave.
    Last edited: Oct 17, 2006
  6. Oct 17, 2006 #5


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  7. Oct 17, 2006 #6
    And water isn't really electrically neutral. It has a permanent dipole moment.

    High voltage lines do not hum (as far as I know), but they can crackle during a low level corona discharge scenario. It's the transformer that hums, really. The transformer has concentric dieletrics throughout the ferromagnetic material to prevent eddy currents from flowing. These get loose and start buzzing
    Last edited: Oct 17, 2006
  8. Oct 17, 2006 #7
  9. Oct 17, 2006 #8


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    How about the air movement from "ion wind", such as propels a lifter? Not sure a high voltage speaker is necessarily a good idea though...

    moo (moo') adj. Of no practical importance; irrelevant, such as a moo point (i.e. a cow's opinion).
  10. Oct 17, 2006 #9
    lol, there's the "engineering hurdle" I mentioned. Engineers always need to have safety in the back of their mind.

    And the ion wind technique seems like what they implemented in that publication from the 60s.
  11. Oct 17, 2006 #10
    What's so good about motionless speakers anyway?

    EDIT: apart from the obvious of no moving parts...
    Last edited: Oct 17, 2006
  12. Oct 17, 2006 #11


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    While I always love to see new ideas, and it's probably possible in some manner to achieve this one, it seems at this point that it would have considerable disadvantages over a normal cone or piezo unit. I'm thinking primarily of the sheer complexity of trying to maintain a zone of plasma or such in the working area.
  13. Oct 17, 2006 #12


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    How about this: http://www.prisonplanet.com/audios_the_next_big_thing.html

    Their description is different from what I had heard before. I thought it was a phased-array and you heard the interference pattern. Regardless, since the source is ultrasonic, the speakers can be flat, thin, and will not appear to move, at least as far as human perception goes.
  14. Oct 17, 2006 #13


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    one advantage to a motionless speaker is you could "hide" it in a unsuspecting spot and it wouldent be noticeable (not like a very large cone)

    i saw on the tv show future weapons that they had a "uni-directional" speaker. supposedly they use it for very loud, directed annoying noises for advancing/ dangerous hostiles.
    anyways, it seems to be a large object, but VERY thin (compaired to a cone speaker) although i have no idea how they work. i should research this.
    this uni-directional speaker, when moving appears to have no moving parts. or it could be like the new "flat" speakers which use a manget and a pice of electrically charged magnetic "foil" to move the air. but apparently these are not uni-directional. so i dont think these 2 speakers are related.
    i have no idea.
    pardon my spelling and grammatical errors.

    "If I have seen further, it is by standing upon the shoulders of giants." -Isaac Newton (1642–1727)
  15. Oct 17, 2006 #14

    What you are talking about is possible.

    The effect is called dielectrophoresis or (if I remember correctly) magntophoresis.

    What you need is a large gradient of either a magnetic field or electric field (think point). Due to the large gradient of the field the force on one end of the molecule will be different than the other end of the molecule and thus a net force will arise. Be warned if using electric fields producing a large gradient and NOT producing corona discharge or arcs is a tricky business.

    I would suspect that the efficency of this sort of setup would be dismall at best.
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