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New Energy (Audio)

  1. May 3, 2010 #1
    I have idea, audio is vibrating wave of air, we know how to make energy from movement (movement energy) very loud audio can vibrate membrane and from that vibrating we can make energy (axiom of movement energy) but that quantity of energy is minor
     
  2. jcsd
  3. Jun 25, 2010 #2
    hi,


    yes that is true, and yes that energy is very minor, that is basically a microphone though, isnt it?, i wouldnt call sound a form of energy, where would the loud sound come from? there is no point generating sound by using energy and then converting that sound into energy again, is there?
     
  4. Jun 25, 2010 #3

    sophiecentaur

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    A fair idea, in principle, but the devil is in the actual numbers - as in many engineering problems.
    When you consider that a tiny battery in a hearing aid can give an (hearing impaired) user an audible signal in their ears for several days, you will have a qualitative idea of how much energy is actually available from sound (by thinking in reverse). An environment in which there would be enough sound energy to make it worthwhile converting it into another form ( say electricity) would be so loud as to be painful or worse.
    It is, I suppose, worth considering 'extracting' the sound energy that exists inside heavy machinery but improving the actual efficiency of a machine would probably be of better value in terms of energy use. We would be talking in terms of energy quantities of the order of those used in solar lights for gardens etc. rather than providing a serious amount of electrical energy.
    But don't give up on inventing novel energy conversion ideas - after all, those damned parking meters are driven by solar energy nowadays and we all LOVE them, don't we?
     
  5. Jun 25, 2010 #4
    Well, you could operate your computer with your voice instead of moving a mouse and keys.
     
  6. Jun 25, 2010 #5

    sophiecentaur

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    You could CONTROL it by voice but you wouldn't be supplying the power to drive it.
     
  7. Jun 25, 2010 #6

    Borek

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    This question shows up again and again. My guess is that's because of the powers installed in audio amplifiers. It is nothing unusual to see 2x100W, which suggests amount of energy that can be harvested from the sound should be of the same order of magnitude. But it is not.

    Honestly - I have no idea why. The only thing I can think off is that our method of producing sound is incredibly inefficient.
     
  8. Jun 25, 2010 #7

    sophiecentaur

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    You are right. Good quality sound reproduction is very inefficient compared with just rubbing your back legs together (if you are a cricket).
     
  9. Jun 25, 2010 #8
    The motion of air molecules is very erratic, a lot of kinetic energy is lost.
     
  10. Jun 25, 2010 #9
    I wouldn't want to try and power my computer with a hand crank, little yet my vocal cords. I am talking about a smaller amount of energy, the movement of a mouse.
     
  11. Jun 25, 2010 #10

    Borek

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    Lost? To what?
     
  12. Jun 25, 2010 #11
    Lost to us, not to the universe. :)
     
  13. Jun 25, 2010 #12

    Borek

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    Explain how it is lost, I have no idea what you mean.
     
  14. Jun 25, 2010 #13
    Lost by increasing entropy. For example if you had a sealed container with 100W speaker in it you could transfer the energy in its entirety to another speaker that would not require another 100W amplifier.
     
  15. Jun 25, 2010 #14

    Borek

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    Still no idea what you mean, nor how it is related to the fact that motion of air molecules is erratic.
     
  16. Jun 25, 2010 #15
    Using a fan to push a book off the table wastes a lot of energy.
     
  17. Jun 25, 2010 #16

    Borek

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    It has nothing to do with the fact that air molecules motion is erratic.
     
  18. Jun 25, 2010 #17
    Sure it does, you use 100W to accelerate a membrane at a very high acceleration, then that energy is distributed into the air all around you, now try to collect all that KE again as it escapes in every direction as far as miles away at the speed of a bullet.
     
  19. Jun 25, 2010 #18

    Borek

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    Fact that energy escapes in every direction has nothing to do with the fact that molecules motion is erratic. It is based on macroscopic properties of the medium, not on the microscopic mechanism. You don't have erratically moving molecules in solids, yet the sound travels in every possible direction, very similarly to what happens in gas.
     
  20. Jun 25, 2010 #19
    Ok, the point is the energy is in the KE of the air molecules and is not easily collected.
     
  21. Jun 25, 2010 #20

    russ_watters

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    Energy in moving air is lost to heat, due primarily to viscous friction in the air and absorption by objects.

    In addition, sound tends to be somewhat omnidirectional, so it is difficult to capture a significant fraction of the ouput of a speaker unless you surround it.

    Also, a home amplifier that delivers several hundred watts is truly earsplitting in a small room, when playing loud sounds. But when your TV speakers are delivering sound that you can talk in a normal conversation overtop of, the speakers are putting out single-digit watts of power. So it isn't just that sound is tough to capture: it is also that there just plain isn't much energy in most day-to-day sounds.
     
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