By Henry Lau 劉以軒

Have you ever thought that it was cool to have a really deep and husky voice like Darth Vader or Batman? What if we could temporarily change our voice for fun? Listen closely – I am going to let you in on a little not-so-secret secret…the power of helium. Being the first in a group of elements dubbed the noble gases, you’d think that helium would be a dignified sort of element. Indeed, helium is well known for its inertness, a property unique to noble gases, which is essential for its use in industry. However, helium can also be used for comic effect: upon inhaling helium, one’s voice becomes squeaky and seemingly higher pitched. This phenomenon is called “helium speech”. So, I guess I lied; you won’t sound like Batman, but you will sound like a Mickey Mouse impersonator! You may have seen people do this in parties or on TV, or even during classes, for its great entertainment value. Next time you want to go incognito, you could try this out. Now, what exactly is it with helium that produces this property?

Before we delve into the mechanism of helium speech, here’s some background information about helium. Helium was first discovered in 1868, when scientists were studying the Sun [1]. When light from the Sun was resolved into a spectrum, a previously undocumented line in the spectrum was observed. Scientists then pursued this further and proved the existence of helium in 1895. Denoted by the chemical symbol “He”, helium is the second lightest element known to humans. Subsequently, helium was found to be very inert, which means it rarely undergoes chemical reactions with other substances.

If you’ve heard someone speak after inhaling helium, you may describe their voice as “squeaky”. But in reality, helium doesn’t change the pitch of your voice; rather it messes with the timbre (or quality) of your voice [2]. In order to speak, your vocal cords have to vibrate, which causes the air nearby to vibrate at the same frequency, termed the fundamental frequency. This also creates a set of weaker harmonics (or overtones), at frequencies which are the integral multiples of the fundamental frequency with lower amplitudes. As those frequencies pass through the vocal tract, they are all amplified (in terms of amplitude, or loudness) due to the vocal tract resonances, but to different extents. Some frequencies tend to be amplified more, which make up spectral peaks called formants, if shown in a power-frequency graph. It is the profile of the set of sound waves produced at multiple frequencies with different amplitudes (and hence the resultant waveform) that make up the quality of one’s voice, known as timbre.

Since sound travels much faster in helium than it does in normal air, when we inhale helium and speak, the resonances and formants shift towards higher frequencies [2]. In other words, the frequencies of the fundamental and harmonics remain unchanged because the vocal cords still vibrate at the same frequency, but the harmonics at higher frequencies are preferentially amplified to a greater extent. On the other hand, if one inhales sulfur hexafluoride and speaks, their voice will sound very deep. This is because sulfur hexafluoride, a heavier gas when compared to atmospheric air, will cause the lower frequencies to resonate more, producing an opposite effect [3].

The production of human speech is a very complex process. But now, we know we can mess with our timbre simply by inhaling gas. Notwithstanding its entertainment value, inhaling helium can also be dangerous. Firstly, helium should not be directly inhaled from gas canisters, as the high pressure can be dangerous [4]. Instead, you can breathe it in safely through a balloon. And while sounding squeaky can be fun, it’s also not advisable to inhale too much helium in one go or for too long as your body needs oxygen to survive. So if you do decide to play with helium, be sure to take necessary precautions and stay safe.

References:

[1] Hwang, J. (2020, August 22). Chemistry of Helium (Z=2). Retrieved from https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_18%3A_The_Noble_Gases/Z002_Chemistry_of_Helium_(Z2)

[2] Wolfe, J. (n.d.). Speech and helium speech (and very brief notes about the physics of the voice). Retrieved from https://newt.phys.unsw.edu.au/jw/speechmodel.html

[3] Harvard University. (n.d.). Helium and Sulfur Hexafluoride. Retrieved from https://sciencedemonstrations.fas.harvard.edu/presentations/helium-and-sulfur-hexafluoride

[4] Josefson D. (2000). Imitating Mickey Mouse can be dangerous. BMJ, 320(7237), 732.