LINGUIST List 2.823

Mon 25 Nov 1991

Disc: Helium

Editor for this issue: <>

Directory

1. Peter Ladefoged, Re: 2.820 Queries
2. Howard Geyer, Re: helium
3. , Re: 2.820 Queries
4. "Mimi Klaiman", Inquiry about helium
5. , helium

Message 1: Re: 2.820 Queries

Helium speech has (among other things) formants with higher
frequencies because the speed of sound is faster in helium
than in air. Formant frequencies depend on the resonances of
the vocal tract. The resonances depend on such things as the
length of the vocal tract. For example, the lowest resonance
in a neutral (schwa) vowel has a wavelength that is 4 times
the length of the vocal tract. If the vocal tract is 17.5 cm
long the wavelength will be 70 cm. The frequency (f) of a
sound depends on the wavelength (l) and the speed of sound
(c) in accordance with the formula: f = c/l. So in a
neutral vowel f = 35,000 / 70 = 500 Hz.
If the speed of sound goes up and the wavelength remains the
same (because the vocal tract dimensions remain the same),
the frequency must also go up.
All that is more than you want to tell you students. Just
say it is because the speed of sound is faster in helium.
Peter Ladefoged (idu0pnluclamvs.bitnet)

	The reason one's voice sounds higher after inhaling helium is related
to the lighter density of helium compared to nitrogen, the primary constituent
of air. The atomic weight of helium is much less than that of nitrogen, and
waves travel at a higher frequency through a less dense medium than a more
dense one. Consequently, the sound waves emitted upon speaking into helium
emerge at a higher frequency.
Howard Geyer
Department of Psychology and School of Medicine
University of Pennsylvania
geyercattell.psych.upenn.edu (Internet)

Message 3: Re: 2.820 Queries

This is a reply to Aaron Broadwell's (hi, Aaron) question about why breathing
helium makes "your voice go up." The answer is that the frequencies at which
the air inside your vocal tract resonates are directly proportional to the
speed of sound. Since sound travels faster in air in which helium has been
mixed, the frequencies of all the vocal tract resonances will be higher.
John Kingston
kingstoncs.umass.edu

In answer to Aaron Broadwell's query about helium
making one's voice go up, I'm pretty sure it's an
instance of Graham's Law of Diffusion; the velocity of
helium is faster than that of air, and since velocity is
proportional to frequency, using helium as a medium
for a soundwave to travel on will result in the wave
frequency being higher than it would in air. I won't swear
I'm right on this, but I think that's the reason.
Mimi Klaiman

Because helium is a lighter gas than air, the speed of sound in it is
greater. Your vocal tract creates (i.e. filters out all but) waves at
certain wavelengths -- which will have a higher pitch (more waves per
second) since they are travelling faster in helium.
John O'Neil