Inhaling helium

[chilehed]

Anyone know the reason it raises the pitch of your voice?

The only remotely plausible reason I've heard is that the lower density raises the resonant frequency of your vocal cords, but I don't buy it. I'd expect the density change to just lower the damping, which would raise the amplitude but not change the frequency.

 

[Locrian]

No, reducing dampening in a vibrating system definately will increase the frequency. I'm honestly not sure whether that is the correct reason though.

Here is what a quick net search turned up:

http://physics.about.com/cs/acoustics/f/heliumvoicesque.htm

 

[Deamiter]

Right now, I'm doing experiments to take pictures of the airflow through organ pipes using schlieren techniques. How I do it isn't very important here, though I think it's quite cool.

Anyway, I am using three different gasses, air, sulfer hexafluoride (SF6), and carbon dioxide (CO2). The index of refraction of air (directly related to density) is 1.00029, CO2 is 1.00045 and SF6 is 1.00075 (SF6 is about twice as dense as air). The air drives the organ pipe at about 300Hz, CO2 drives it at about 220 and SF6 drives it at about 150Hz (plus or minus about 10 Hz to account for edge tone effects).

Clearly the density of the medium has a great impact on resonance frequency as the organ pipe is run at its fundemental in each case. I could look up equations for you, but only if you ask as I get the feeling you're not really trying to figure the numbers.

Basically the density of the medium is a key factor in determining the resonance frequency. It actually has a much smaller affect on amplitude (almost unnoticable in my organ pipes).

 

[chilehed]

Well, yes, damping does have an effect on frequency in a spring/mass system (like a guitar string), but the viscosity change is so low between air and helium that I'd not expect it to change the resonant frequency of the vocal cords a much as we hear.

But the light just went on when you mentioned organ pipes, Deamiter. I'd never considered the fact that the lungs form a resonance chamber to amplify the sound, and, although the order content of the cord vibration probably won't change, the frequencies amplified by the lungs certainly would. The amplification would get shifted an octave up and the lower frequencies would get filtered out - sounds like a recipe for a funny voice.

If I still worked in the lab I'd do some after-hours experimentation - but no matter, this sounds very plausible.

Thanks.

 

[Deamiter]

Exactly right, except that the resonance cavity is actually in your mouth and throat, not your lungs.

 

[Novasonic]

As you all know, when you talk without helium in your lungs, your voice has a certain pitch range, and that range is determined in part by the density of the air that you are exhaling. The higher the density of that air, the lower the pitch and the faster is the speed of sound. So if you talk while exhaling Helium, which has less density than air (which is roughly 78% nitrogen), the pitch of your voice rises.

Does this help at all?