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How would music sound in a different atmosphere?

  1. Apr 27, 2015 #1
    I guess that the way we experience sounds on Earth is very importantly influenced by the composition and density of our atmosphere, since it determines how a pressure wave will be formed and will propagate.

    Does music sound appreciably different when heard at very high altitudes with low air density? Or opposite, with higher than normal air density?

    How would a different atmosphere composition and density affect the way we hear sounds and music?
  2. jcsd
  3. Apr 27, 2015 #2


    Staff: Mentor

    Have you heard sounds under water?
  4. Apr 27, 2015 #3
    Yes sure, I guess I posted a rather silly question o0)
  5. Apr 27, 2015 #4
    Frequency, wavelength, and velocity are interrelated by f=v/λ so if you have a fixed sound with a given wavelength, and you increase velocity, then you're going to increase frequency or pitch.

    This paper may help... (assuming it's correct, I haven't carefully reviewed it, and it appears it's a lower-level physics class, not written by a PhD student)

  6. Apr 28, 2015 #5
    The frequency of reed instruments depends upon the density of the gas as well the density of the reed.

    The dependence on frequency of a string instrument is only slightly dependent on density. A plucked string will vibrate longer in a thin atmosphere and sound weaker;the frequency is certainly not proportional to the density of the surrounding gas. A plucked string has finite frequency in a vacuum.
  7. Apr 28, 2015 #6


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    Staff: Mentor

  8. Apr 29, 2015 #7
    vocal "cords" and reeds are physically similar
  9. Apr 29, 2015 #8
    Hmmm.... I've been giving this more thought...

    it makes sense that a reed's vibrations is dependent on the density of both objects, and likewise the air density NOT having much of an effect on a string...

    What about a speaker? It seems more like it would be analogous to a string... A speaker's movement is controlled by the signal driving it (instead of the tension and mass of the string), and the "rate" would be independent of air density, but the displacement with each travel obviously would change depending on air density and the voltage amplitude driving it, at least in theory I think a "thick air" would require more power to push the driver the same displacement...

    Suppose I have a breathing source and I was in a room full of another gas, such as helium since we've probably all inhaled helium (and I'd guess not many of us have inhaled sulfur hexafluoride - but as an FYI, inhaling N2O, which is also denser than air (but I don't think nearly as much as sulfur hexafluoride) also results in an audible "pitch lowering" effect). Then, suppose we sent a 100 Hz sine wave to the speaker. Regardless of the density of the medium, as long as there is "a" medium to transfer the pressure changes and the amplitude was enough to move the medium such that it could move my tympanic membrane (and thus everything else in my ear) by the time it gets to me, then wouldn't I still hear 100 "pressure changes" per second, which my ear would detect as the same pitch as if the speaker and I were in a "normal" atmosphere? Better yet, to eliminate any of the differences in passing from one medium to another regarding the path in our ears, suppose we hooked a microphone to an o'scope... Wouldn't it still read 100 Hz regardless whether it was air, helium, sulfur hexafluoride, N2O, Butane, etc.? And if our ear (pitch) works on "pressure changes per second" then wouldn't we hear it at the same pitch whether it was helium vs. air between the speaker and your ear? The sound may travel faster in different mediums resulting in each pressure change getting to our ear from the source in a shorter time, but the number of pressure changes per second at your ear would be the same as they would be at the speaker, which is the same frequency as the voltage going into the speaker. Right??? I still feel like I'm missing something...

    Does the apparent change in pitch have anything to do with the fact that there are two different mediums at play, first through helium in the persons lungs transitioning to air? OR, is it all related to what you said about vocal cords being more like a reed than a string or "cord" ?

    I know I am somewhat contradicting my previous post...
    Last edited: Apr 29, 2015
  10. Apr 29, 2015 #9
    Listening under water to a speaker that's under water will just be a regular (albeit wet) experience.
    The reason why people sound like chipmunks when inhaling helium is mostly because your whole mouth is a resonance cavity. Because of c=λν, since c has changed now, the frequency ν at which the resonance happens has shifted as well. Effectively, it makes it sound as if your mouth was suddenly several times smaller, the sound of which we obviously associate with very small people (chipmunks).
  11. Apr 29, 2015 #10
    @rumborak that's a good explanation... summing it up with, "as if your mouth was suddenly...smaller" seems to be a good analogy. Never thought about it that way...

    As to the OP's question, "music" from a speaker would not change... Right? But instruments which rely on resonant air columns for their different notes, like woodwinds, would likely change significantly... So if you took something like a saxophone into an environment twice as dense (and you also breathed that air out into the instrument), it would sound as if it had a resonant cavity with twice as much volume... so it would give one octave lower, half the frequency?
  12. Apr 29, 2015 #11
    The resonance cavities act as frequency filters on the "input signal" that comes from the reed. So, yes, the resonances selected would be an octave lower, but assuming the input signal wasn't just white noise, the resulting signal won't just be a perfect downscaling of the regular saxophone tone, but instead a hybrid of original reed signal filtered by low-frequency resonances.
  13. Apr 30, 2015 #12


    Staff: Mentor

    In the Florida Keys every summer, they hold an ipunderwater concert. If the sound was distorted, people wouldn't attend.
  14. Apr 30, 2015 #13
    on a separate note, people that do SPL competitions with loud car stereos can only hit 180-190 dB because of the atmospheric pressure we are limited in manipulating. supposedly a different pressure would change that limitation.
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