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We all know the silly effect that inhaling helium has on speaking and singing, where some wacky speed-of-sound physics makes our voices sound unnaturally and ridiculously high-pitched. A student asked me today what would happen if the same thing was tried blowing into a trumpet. What would the result be?

I was not comfortable instructing kids to try it out, as I'm sure deliberately inhaling helium must violate some sort of school safety rule. But it could make an interesting special effect and I'm intensely curious. Has anyone actually tried it?

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  • You'll also find that if, having drunk a fizzy drink, you burp into the instrument while playing it that the pitch drops. This is because the speed of sound in Carbon Dioxide is significantly slower (267 m/s) than in air (343 m/s). Sound travels much faster in Helium (1007 m/s). See this table for the speeds in various gases: pages.mtu.edu/~suits/SpeedofSoundOther.html Oct 26, 2021 at 13:32
  • There's enough of a density difference between cold air and warm air that a cold instrument will be noticeably off pitch until it warms up. Oct 26, 2021 at 23:47
  • Random idea: Write a piece that instructs the wind and brass players to breathe helium while playing certain passages.
    – Divide1918
    Oct 27, 2021 at 8:58
  • @Divide1918 you are evil! Oct 27, 2021 at 17:00
  • And insist that it be played in tune.
    – nuggethead
    Oct 27, 2021 at 21:01

2 Answers 2

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OK, I'll do your Googling for you :-)

(There's one for trumpet too, but I thought a Helium Tuba might be even more fun.)

In the video, a tuba player uses a modified mouthpiece to inject helium into his mouth while playing. On a sustained note, the pitch rises by nearly an octave while the helium is being injected; once the helium is no longer being injected, the pitch slowly falls back to the expected pitch over the course of a few seconds. Melodies become quite difficult to play since the resonances of the instrument are constantly changing, and the player even has some difficulty with scales.

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In addition to Laurence's answer: it's worth to note that the reason why the pitch of a wind instrument changes is different from why the voice sounds differently with helium.

In a wind instrument the source of sound is a vibrating air column, and the frequency is proportional to the speed of sound, see https://en.wikipedia.org/wiki/Acoustic_resonance#Resonance_of_a_tube_of_air . As the speed of sound in Helium is almost 3 times larger than in air, in pure helium the pitch would be almost an octave and a fifth higher than in air.

On the contrary, in human voice the source of the sound are vibrating vocal folds, and their vibration frequency doesn't depend on the gas medium. However the wavelength in helium does change, and it affects how various frequencies interact with your throat and mouth resulting in a different timbre. See this question for more detailed explanations: https://physics.stackexchange.com/questions/122353/why-does-our-voice-sound-different-on-inhaling-helium

Finally, while helium itself is harmless, there are indeed safety considerations when breathing it, especially from a pressurized container, including risk of asphyxiation, mechanical damage and others, see e.g. https://www.healthline.com/health/inhaling-helium . Insides of balloons are often coated with talcum powder which (in large amounts/regular exposure) can cause lung issues.

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    "the reason why the pitch of a wind instrument changes is different from why the voice sounds differently with helium" -- in the case of the voice it is vocal chords, and in the case of a trumpet it is the lips that are the source of vibrations; then the cavity resonances are dependent upon the properties of the gaseous medium and the nature of the cavities. What is different between these two cases?
    – user39614
    Oct 27, 2021 at 2:51
  • @exnihilo good question (actually it would made a good separate question). In Tuba indeed the primary source of vibration is a reed formed by the musician's lips, but it is coupled to the the pipe of the instrument, so the frequency of vibration is determined by the length of the pipe. Human voice is more of a free reed instrument like harmonica. Cavities in vocal tract can absorb various frequencies, but they are not coupled (at least not via air impedance) to the vocal folds and don't change the frequency which they vibrate. Oct 27, 2021 at 3:51
  • It's not quite that simple -- with practice you can "force" a pitch that is not a harmonic of the musical instrument's length/bore profile. The combination of vocal cords and mouth is less dependent on the "length" because it's such a short length & relatively wide bore. Compare with a brass player warming up with just the mouthpiece, where the pipe length is pretty much irrelevant, being a small fraction of the wavelength Oct 27, 2021 at 17:03

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