That helium makes your voice squeaky is known to everyone who joyfully discovered this little trick while playing with helium balloons as a child. In a sense we are all, then, highly fortunate that the inert and harmless helium was discovered and manufactured in large amounts in the twentieth century – it was intended to take the place of hydrogen, which was highly flammable and therefore in no way useful for children’s parlour tricks. But none of this answers the question most people eventually ask after getting over the fun of it: Why does your voice get squeaky, in the first place?
– Helium –
Helium, which is known as a noble gas or an inert gas because it does not react with other elements under normal conditions, is one of the most common elements in the universe. Stars produce it in massive amounts through hydrogen fusion, and it is also present in substantial amounts in the atmospheres of the planets Jupiter, Saturn, Uranus, and Neptune.
On Earth, the majority of our stored helium was harvested during extraction of a more valuable chemical, natural gas, from subterranean reserves. The United States has become a leading supplier; in addition to private production of helium, a considerable amount is still being drawn out of massive Cold War reservoirs initially created by the government as rocket coolant reserves.
– Speech –
The reason helium makes our voice squeak is because of how it interacts with our vocal cords. These are a set of folding tissues in the throat which air passes through as we breathe. The sounds that we interpret as speech, or words, are produced by vibrations within these cords. Faster vibrations produce a higher-pitched sound; slower vibrations produce a lower-pitched sound. This is the first part of speech: producing audible sounds in the throat. The second part, forming the actual words themselves, is accomplished in the mouth, by moving around our tongue, our lips, and the position of our teeth so that the sound is modified.
In essence, then, there are actually two parts of speech: the sound being produced, and the sound being modified. It is the vocal cords which are responsible for the production part of speech.
– Helium and Speech –
Normally, our vocal cords produce regular, predictable sounds (which is why we are able to speak in a normal voice, as well as to do things which require much finer control of the vocal cords, like singing). They do this because they are specifically tuned to function in normal air – that is, the usual mix of gases which make up the atmosphere of the Earth – and to produce a particular sound by vibrating that air current at a particular frequency.
Helium, however, is not normal air. In particular, it is far lighter: The atomic mass of nitrogen and oxygen is 14 and 16, respectively, but the atomic mass of helium is just 4. (In chemical terms, a helium atom consists of just two protons and two neutrons, whereas oxygen has eight of each.) This means that the same vibrations in the vocal cords will have more of an effect on the lighter helium – the sound will travel faster, emerging not as full and deep but thin and squeaky.
Helium is not only the best gas to try this little trick with, but the only one – only hydrogen and helium are lighter than air, and hydrogen is dangerous: It can explode when it contacts oxygen. However, if you were to try the same trick with a heavier noble gas, like argon or krypton (not radon – it’s radioactive), the effects would work in reverse: your voice would become slower and deeper, rather than higher and squeakier.
