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Why does my voice change when I talk into A fan.

  1. Jun 10, 2005 #1
    It is really hot, and humid here. I have my fan running almost constantly. Ever since I was a kid (well I am still kind of young) I have talked into my fan and got a kick out of hearing my distored alien voice. I was wondering what is the physics behind this distorsion? I was thinking that the sound waves just simply get bounced back at different times since the blades are kind of behind each other on each pass, and since its going so fast you can hear the effect. I am probably way off but thats all I could think of.

    Another thing why is it that I feel cool when the fan is on? I was thinking that it pushes all the humidity, and gas away from where I am providing a lower density of air, and water which would mean less energy in that area and less heat. Is that right?
     
  2. jcsd
  3. Jun 10, 2005 #2
    I am assuming yor are running just fan without air conditioning.
    first of all, it is likely that air temperature is lower then body temperature.
    So fan constanly forces warm air near your skin out and pushes colder air to your skin.
    then, the air near you skin is also more humid because skin is always moistured by the sweat. So air humidity near the skin is usually higher, so dryer air forces the sweat to evaporate more thus cooling your skin a little.
     
  4. Jun 10, 2005 #3
    Not sure about the first part of your question (I'll put the fan on at work tomorrow and experiment) but the second part is almost certainly due to the fact that 'evaporation causes cooling'. You are sweating as it is hot, and the fan increases the rate of evaporation of this sweat. This evaporation causes cooling - similar to when you step out of a shower and straight away feel cool.
     
    Last edited: Jun 10, 2005
  5. Jun 10, 2005 #4

    Pengwuino

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    haha i always use to do that! Ok guys what hes doing is... get one of those normal standing room fans in the little cages and go right up to it and talk into it. It'll sound like bits of hte voice are being completely removed so it sounds a cartoon character talking while being grabbed and shookd by the neck.
     
  6. Jun 10, 2005 #5
    You talk to fans!!
    :surprised

    (Sadly, I'll be doing this at work tomorrow ) :rolleyes:
     
  7. Jun 10, 2005 #6

    Pengwuino

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    Better then talking to my refrigerator
     
  8. Jun 10, 2005 #7
    What do you say to it.. "chill out"?
     
  9. Jun 10, 2005 #8

    Pengwuino

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    haha... yah...
     
  10. Jun 10, 2005 #9
    Wow I was way off. Thanks though. Please do conduct your experiment tomorrow so I will know why I sound like an alien/some kind of robotic chimpmuk.

    This is the type of fan I am talking about.

    http://home.uchicago.edu/~heinrich/FAN.gif
     
    Last edited: Jun 10, 2005
  11. Jun 10, 2005 #10

    Danger

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    Yeah, Adrian. Also please post pictures so I'll have some reason to razz you besides just your dancing beet avatar.
    I've never heard of this effect before, but I'm wondering if there might be a multiple Doppler shift due to the shape and speed of the blades or even just the incoming airflow speed alone. Does it also do so from the back of the fan? I know that shouting at someone in a heavy wind alters the sound because the compression wave partially follows the direction of the air that it is propogating through.
     
  12. Jun 13, 2005 #11
    Your voice has a frequency, and so does the fan. These frequencies combine to produce the sound of your voice through a fan.
     
  13. Jun 13, 2005 #12
    It almost sounds like it is reducing the frequency of my voice since my voice sounds kind of choppy, and not continuous. I know the frequency of my voice can't change by talking into the fan. How do they combine? I am kind of confused about that. After reading what you wrote I am thinking that as I go closer to the fan only some of the sound waves from my voice make it through since the blades are moving so fast, and that is why I hear my choppy voice.
     
  14. Jun 13, 2005 #13

    OlderDan

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    I believe this is primarily an amplitude modulation effect. The sound of your voice is being reflected from the fan blades back to your ears with more intensity than the sound that finds its way to your ears via internal paths and direct air paths. It is comparable to singing in the shower, except that the shower has much more surface and might have some resonance effects. Every passing blade is going to raise the intensity level compared to every place between blades. It is of course complicated by the shape of the blades and the direction of the reflections, but the rotating blades will surely result in a periodic reflection function. There will also be some timing effects from the shape of the blades and some small doppler effect because of the moving air and a velocity component of the blade in your direction.
     
  15. Jun 13, 2005 #14
    I did this same thing too when I was a kid. California was very hot without air conditioning. I have to read over OlderDan's post again, I always thought the reason was what Monzart said in his first post.
     
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