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B Hardware that can produce sound waves with frequencs 0-200hz

  1. Dec 11, 2016 #1
    i'm doing an experiment to study the effect of sound waves on fire and smoke and would like to know how can i produce sound waves with frequencies varying from 0-200 hz
     
  2. jcsd
  3. Dec 11, 2016 #2

    davenn

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    I am sure there is software you could use on your computer and get an output from your sound card

    a couple of programs I have for that are NHC Tone Generator and Wavgen
    you will find them on google to download


    Dave
     
  4. Dec 11, 2016 #3

    anorlunda

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    :welcome:

    Those big refrigerator size speakers that they use at rock concerts do a good job over much of that frequency range, but not down to 0 hz.

    Better still would be a stream of compressed air with a rotating disc with holes in front of it. With that you can adjust:
    • The pressure of the compressed air
    • The flow rate of the compressed air
    • The frequency by changing the disc speed and also by varying the number of holes in the disc.
    • You can make the whole thing portable and you can aim it and vary the distance to the fire.
    For exactly zero hertz, take away the disc and blow air directly on the fire. But if you tell the guys in the firehouse that you need to study that, you'll be laughed out of the house and never invited back. Shame on you for writing 0 hz in the OP.
     
  5. Dec 13, 2016 #4
    Anorlunda. I originally thought you were wrong that a small hole could produce low frequency sound radiation when it is only a small fraction of a wavelength in diameter. But sound is a longitudinal wave and, unlike a loud speaker, the rear of the "piston". which would radiate cancelling radiation, is not open. But it still leaves me wondering, because as receiver of sound, I cannot yet believe that a small hole will be an efficient receiver of energy.
     
  6. Dec 13, 2016 #5

    anorlunda

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    Who said anything about small holes? When I wrote that I visualized 1 inch diameter holes. Unlike a siren, I visualized something that generates discrete puffs of air pressure.

    Years ago, I walked closely in front of one of those rock concert speakers. I was amazed at how I could feed the compression waves in my chest. That taught me to remember that sound is nothing but pressure waves. At low frequencies, your body becomes a better sensing organ than your ears.

    The ultra low range 0-200 hz you gave in the OP is problematical. At the high end it produces audible sound, and ordinary rules of sound propagation apply. At the low end, it is more like gusts of wind, or shock waves from nearby explosions. In the middle frequency ranges is a transition zone where it becomes unclear which model best applies, the siren or the air puffer. It sounds like your thinking is stuck in the audible sound end of the spectrum. You have to get your head around both to succeed for that entire range.

    There are three parameters you can play with on the disk. Rotation rate, number of holes, and hole diameter. That sounds pretty rich in terms of being adjustable.
    You may need different combinations of those parameters to cover all the sub-ranges in the 0-200 spectrum. Fortunately, is sounds easy and cheap to produce a number of discs to experiment with.

    There is another critical parameter that you did not mention in the OP; distance to the flame. You said it was an experiment. Research rather than development. If so, then you may be able to investigate the effects at very close ranges only. If the research results are positive, then you could continue trying to make a long range device that uses the principle.

    One final piece of advice. Search the literature before building equipment. It sounds hard to believe that your topic has not been researched before.

    Good luck. Perhaps in the future you could post here on PF how your experiment turned out.
     
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