Why do people's voices sound so high-pitched when they inhale helium?

Gnomon

Sound travels faster in helium than it does in normal air, because helium is less dense than normal air. The wavelength of the sound produced by your voice is fixed by the size of your mouth and throat. If the speed goes up but the wavelength stays the same, the frequency has to go up too. We hear this as a higher pitch. Nov 19 02, 4:02 PM

Gnomon's logic is wrong. *The speed of sound a: A primary means of information traveling in a media by propagation of locally pressurized compression, i.e., pressure waves. Thus, a denser material can transfer the information on the local pressurization more efficiently and faster. The speed of sound is faster in a denser medium. http://www.mengr.tamu.edu:70/thermal-fluidsciences/kkihm/mfhtl/classnote/Gasdynamics/Lecture-3-4.doc Helium is in fact less dense than normal air, making the speed of sound slower. According to this site http://www.straightdope.com/mailbag/mheliumsqueak.html the reason our voices change when we inhale helium is noy because the frequency of the sound changes, but because the timbre changes. It goes into much more detail. To see the speeds of sounds in different mediums, go to http://www.ststephens.wa.edu.au/subject/physics/12physics/units/Sound/Sound_Waves_Intro/ I hope this answers your question :) Nov 19 02, 9:46 PM

http://www.straightdope.com/mailbag/mheliumsqueak.html http://www.ststephens.wa.edu.au/subject/physics/12physics/units/Sound/Sound_Waves_Intro/ Don't know why those didn't underscore, sorry. Nov 19 02, 9:49 PM

Gnomon

My answer above is right. The speed of sound in Helium is nearly three times as fast as the speed in normal air. This can be seen on the page at this link: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html#c5 The person who wrote that doesn't know too much about voice formation, however. The vocal cords do not vibrate at one frequency. They act as a noise generator, producing vibrations at a number of different frequencies. The vibration then locks into a resonance mode with the throat, mouth and nasal cavities to produce sound of a particular pitch. This is similar but not the same as the way a sound is produced in a reed instrument such as a clarinet or oboe. In these instruments, the reed is completely free so the sound is determined entirely by the length of the air column. In a voice, the tension in the vocal cords can change so the pitch is partially determined by the tension and partially by the resonance in the air column. As I said before, if the speed of sound is higher, the frequency of the sound goes higher because the wavelength of the resonance chambers are fixed. I explain this in the New Scientist magazine's Last Word column: http://www.newscientist.com/lastword/article.jsp?id=lw422 You can also find a similar explanation in Scientific American, which is quoted on this page: http://barelybad.com/words2_helium.htm Nov 20 02, 9:20 AM

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