[InorganicFilip]

Hi there,

I'm a chemistry student (University of Aberdeen). As a child, sometimes me and my friends used to inhale helium from balloons just for fun. I was wondering if anyone knows how much helium (by volume) one must inhale in order to change his voice? What is the minimum to hear any significant changes in the voice?

Best wishes,
Filip.

[Arkcon]

Hmmm ... kinda an interesting problem.  OK, this is a learning forum, we'd like to see some work from you first.  How does helium change our voice?  What property gives it that ability?  What actually does it do to our voice?  Would less have less effect?  Or none at all?  And how much is safe?

[InorganicFilip]

Hi Arkcon,

How does helium change our voice?

The pitch of our voice is higher.

What property gives it that ability?

Lower density than that of air.

What actually does it do to our voice?

The lower density of helium causes sound to travel faster than in air. This leads to our vocal cords vibrating faster and more often, giving the effect of higher pitch.

Would less have less effect?  Or none at all?  And how much is safe?

The air is constantly being exchanged (replaced) in our lungs and vocal instruments. I think if one breathed a tiny amount of helium, it would not have a significant effect (hardly noticeable and short-lasting) due to the fact that it would mix with the denser air in our lungs. It would be short-lasting because helium would be getting out of our system with each breath.
Unfortunately, I don't know how much is safe. I know that breathing a 100% helium can lead to suffocation.

Do you think breathing a 90% oxygen, 10% helium mix would be safer?

[Arkcon]

Well yes, that's what's used to inflate party balloons, its not pure helium, just enough to help them float.  I suppose the variable density of a variety of mixtures should make for different pitches, from higher to very high, but you'll always have to have some air, or die.

[InorganicFilip]

Well yes, that's what's used to inflate party balloons, its not pure helium, just enough to help them float.  I suppose the variable density of a variety of mixtures should make for different pitches, from higher to very high, but you'll always have to have some air, or die.

Agreed.
Still looking for an answer to my question. Do you know how much helium one needs to breathe for the higher pitch effect? I know it's difficult to answer given the fact that gas mixtures (and their proportions) can vary per tank, but if you know, please let me know too

Best wishes,
Filip.

[mjc123]

First of all, DO NOT INHALE HELIUM. It is highly dangerous to inhale any asphyxiant gas. You do not need to inhale it (i.e. breathe it into your lungs) in order to produce the voice effect.
This forum is pretty strict about giving advice for liability reasons, so I am NOT going to say that the following procedure is safe, nor do I recommend doing it. Only that it appears less dangerous than inhaling a lungful of helium.
Take a good breath of air. Fill your mouth cavity with helium from a balloon. Do not breathe in. Talk like Mickey Mouse for a few seconds. Breathe out, and breathe in air.
Of course if you're talking about a 90% oxygen mixture, that makes a difference!
Maybe you're not that stupid or ignorant, but people might get the impression that to do the trick you have to breathe in helium, which is dangerous.

To address your specific question: how does the speed of sound depend on the density? How does that affect the frequency? How much would you have to change the density of air to raise the pitch by one octave (frequency ratio of 2)? What percentage of helium in air would produce this change?

[Enthalpy]

90% oxygen would be badly hazardous, remember Apollo-1. Use 90% air instead.

How much helium... One half-tone is a 5.9% frequency change (that is, 1.059¹²=2 since Bach), so maybe 20% pitch suffices - no accurate estimate. If you just neglect helium's density (not the biggest error here) and effect on compressibility (monoatomic vs diatomic), 20% velocity change needs a 40% lighter gas, or 40% He and 60% air. A nice but high-tech mix would be 20% O₂, 40% He, rest N₂.

Zero oxygen in the breathed gas isn't immediately noxious. Pilots make such trials to be aware of the effects: euphoria after several breathes, then fainting. The apparatus and your posture should take the helium source away if you faint, so hold the source with your hand instead of a strap, sit on a bed, have an other person nearby - I mean, a friend.

Double-check if helium may dissolve in the blood. I believe O₂ + He is used for very deep diving, to avoid the soluble N₂.

[billnotgatez]

@Enthalpy
Was this empirically determined or calculated?

...
How much helium... One half-tone is a 5.9% frequency change (that is, 1.059¹²=2 since Bach)
...

I am curious!

[Borek]

@Enthalpy
Was this empirically determined or calculated?

...
How much helium... One half-tone is a 5.9% frequency change (that is, 1.059¹²=2 since Bach)
...

I am curious!

Definitely measured, pitch of the notes was established long before we were able to measure the frequency (well, even before we knew there exist something like frequency!).

[billnotgatez]

Thank you for catching my mistake
I misinterpreted what @Enthalpy said
I should read closer