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Why does a whistle sound louder when you blow harder?

  1. Dec 30, 2007 #1
    I've noticed that the harder you blow into a whistle, the louder the sound produced. Why is this? Does the high speed of the air rushing into the whistle increase its vibrational amplitude? Do compressions and rarefactions of the air have anything to do with it?
     
  2. jcsd
  3. Dec 30, 2007 #2
    I would expect that the harder you blow the more dynamic pressure you have in the whistle. This is a form of energy, that gets translated into sound. I would also expect a higher pitch with more energy. However, I do not know anything about acoustics, so my intution could be totally wrong here.
     
  4. Dec 30, 2007 #3
    It is similar to the case when you strike a guitar string, the harder your strike, the lounder the sound it produces, but the frequency is the same. In the case of a whistle, the harder you blow, the higher pressure you exert and therefore the higher the amplitude of the sound.
    I think, when you blow harder, the sound may have higher frequency as well because the air stream is a little bit more dense.
     
  5. Dec 30, 2007 #4
    pixel, not trying to nit pick but having once played a musical instrument, to wit the piano, the harder I strike the key the louder it becomes but it has the same frequency causing much irritation to my piano teacher. I think the same would be true for a trombone player with how hard he blows his horn. This analogy would not apply to a bugle player because he is changing the frequency by changing the shape of his lips. I belive a whistle would have the same properties, simular to a magnetron or klystron, change the size the tuning cavity to change frequency in a whistle. Resonance?
     
    Last edited: Dec 30, 2007
  6. Dec 30, 2007 #5

    dst

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    Because you're effectively producing a standing wave with most musical instruments, the frequency will remain constant but the amplitude will go up with additional pressure/force.
     
  7. Dec 30, 2007 #6
    dst, with a standing wave no energy is transmitted? Please clarify.
     
  8. Dec 30, 2007 #7
    Sure, it's the resonance of the air stream in the cavity. The frequency depends not only on the cavity but the density of the gas stream as well, and the harder you blow, the more dense the air (even though not very much) so you may have heard the whistle sounds at higher frequency when the referee blows very hard
     
  9. Dec 30, 2007 #8
    I have to politely disagree with you. I use as an example the radar klystron. Many times in physics it is shown that audio acts like electromagnetic waves. When I wish to change the frequency of the transmitted energy in a klystron, I first have to change the carrier frequency by changing the crystal of the master oscillator. (Due to the size of the tuning cavity and length tuning screws I can not vary this frequency by very much). After I do that then I have to adjust the tuning screws for the hightest power (unless stagger tuning is used generating a few side waves). No matter how many electrons I pump into the klystron (via the 5VDC heating element) the frequency remains the same. Increasing the the plate voltage increases power but does not change the frequency. We may need smarter minds to settle this riddle.
     
    Last edited: Dec 30, 2007
  10. Dec 30, 2007 #9
    Not quite the same.
    Have you ever seen the experiment of a man breathing helium? Immediately after that he changes the voice and is sounds like from a beautiful woman's mouth! The same cavity: but different voice because of different gas.
     
  11. Dec 30, 2007 #10
    This is true but he said an air compressor, would you suggest that he would be using anything but ambient air that has been compressed in an air compressor for use as the prime mover?

    Changing from atmospheric air to helium is like changing electrons to positrons. Changes the whole picture but the theory still holds true if Helium is given as the gas in the whistle.
     
    Last edited: Dec 30, 2007
  12. Dec 30, 2007 #11
    Well, if you blow very slightly a whistle, we can say the density of the gas stream is just that of the ambient air, but if you blow very hard, it may be compressed a little bit, then the frequency increases, but very little.
    If you have a whistle now in hand, you can test that.

    I have worked with an experiment setup of gas mixuture simulation before, in which the flow is in the range of 10 - 2000ml/m, then I could see the inlet pressure increasing if the flow increased.
    Edit:
    And for normal gas, the density increases proportionally with the pressure.
     
    Last edited: Dec 30, 2007
  13. Dec 30, 2007 #12
    Take it easy, when you blow harder your lips purse together more tightly thus changing the characteristics of the resonant cavity, unless a valve is downstream per example of the horn (better analogy than the trombone). That is called a dead head, can't move until the valve opens.
     
    Last edited: Dec 30, 2007
  14. Dec 30, 2007 #13
    No, the cavity is inside the whistle, not in your mouth isn't it?
    You may also have heard the sound of gas leaking of some types (from a punctured tire let say), the stronger the pressure , the higher the frequency.
     
  15. Dec 30, 2007 #14
    pixel, the resonant cavity is the same as the entire electrical ciruit, less the stable element. The stable element was a analogue compass that always gave true north. All come into play.

    Out of one come many, out of many come one. I don't know where I heard that but think there is a historical basis.
     
    Last edited: Dec 30, 2007
  16. Dec 30, 2007 #15

    RonL

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    The study of a vortex tube, might provide a little insite to whats going on thermally inside the whistle. I think, but don't know for sure that this might be the world's most common use of a vortex.
    How much effect will heat have on the sound you hear ?
     
  17. Dec 30, 2007 #16
    A vortex tube? Did you know that when you cross the equator that the water circulates backwards when you flush the toilet?.


    Send them to schools and buy them books.
     
    Last edited: Dec 30, 2007
  18. Dec 30, 2007 #17

    RonL

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    Guess if i had to make a bet, i'd still put my money on more whistles than comodes -:)
     
  19. Jan 1, 2008 #18
    RonL, it will change the frequency by a little like I mentioned with the Klyston but the human ear will probably not be able to detect the difference without a spectrum analyzer. The resonant cavity determines the frequency but there are side bands that can be amplified but the amplified side band can never equal the power (sound) of the resonant circuit.

    In reference to pixel, of course your mouth is part of the resonant circuit for reasons I have already stated. Your lungs also and the size of your voice box.

    I must clarify after thinking about this, it has been a long time since I worked with radio frequency side bands. With our radar we used side bands to raise the frequency of the crystal master oscillator since a 5GHZ and 10GHZ crystal would be difficult to manufacture, back in the day. ( I have to add app. because it is still classified) app. 5GHZ being the app. frequency of the tracking radar and 10GHZ being the app. frequency of the missile reference carrier wave, semi-passive. Our master oscillator had a base frequency of app. 100MHZ and we amplified the upper side band multible times to get the required transmitted frequency. Back then (40 years ago) these were big secrets. I guess I don't know what I am talking about with a whistle but it seemed to make sense to me.

    In effect I maintain that a Whistle can be compared to a carrier wave Klystron but not a pulse Klystron.
     
    Last edited: Jan 1, 2008
  20. Jan 1, 2008 #19
  21. Jan 1, 2008 #20

    dst

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  22. Jan 2, 2008 #21
    Thanks dst for the article on the pennywhistle. I see your point, comparing a Klystron to a pennywhistle can not be done. But did the original thread starter call it a pennywhistle.

    I used to make a whistle out of a stout blade of crabgrass. Hold it perfictly between two thumbs and blow with all your might. The blade of crabgrass would vibrate (crystal oscillator?) and produce a most annoying sound but the frequency would change if you blew hard or soft and how taut you held it. The lower frequencies were the most annoying. To produce the lower frequencies you eased up on how tight you held the blade of grass how hard you blew. My Dad taught me that, I think he wanted to get rid of the crabgrass. After you got good at it you could even whistle songs but only in five scales. If a different scale was needed then the width of the blade of grass had to be taken into consideration. It was problematic not to break it but there were pleanty of substitutes.
     
    Last edited: Jan 2, 2008
  23. Jan 2, 2008 #22

    dst

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    That wasn't my article, I just quoted someone else's post, just FYI.
     
  24. Jan 2, 2008 #23
    This was not an attack on you but only friendly conversation. I knew you could not possibly write such an article as I equaly could not. I say this becasue some make the premise that you can compare the creation of the universe to a pennywhistle when my comparison was much less extreme.
     
  25. Jan 2, 2008 #24

    dst

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    Don't worry, nothing hostile, I'm just pointing that out ;)
     
  26. Jan 2, 2008 #25
    I do not think it is useful to introduce klystrons and mahgnetrons into the discussion in order to explain a simple whistle.

    Analogies are only useful only if they simplify the problem, not if they complicate things, or introduce many additional factors that need to be considered.

    All this brings to mind whether or not some of the posters have played the instruments being discussed. A trombone player can change the frequency he produces by altering his lips in exactly the same manner that a bugle player can. In their respective cases, the slide and the valves serve to change the length of the resonant cavity.

    As to the topic of the human body being part of the resonant system of the whistle itself... A little girl and a big fat man, both produce the same frequency sound with the same whistle, provided they blow at the same rate. This is DESPITE the fact that their bodies and therefore their "contributions" to the resonant system, are vasty different.

    It's the density of the air inside the whistle that's important.
     
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