Page 4 - Science Focus (issue20)

Helium and Why

It Makes You Sound Like Mickey Mouse

氦氣 - 為何它使您的聲音像米奇老鼠

By Henry Lau 劉以軒

Have you ever thought that it was cool to have seen people do this in parties or on TV, or even during
a really deep and husky voice like Darth Vader or classes, for its great entertainment value. Next time you
Batman? What if we could temporarily change our want to go incognito, you could try this out. Now, what
voice for fun? Listen closely – I am going to let you in exactly is it with helium that produces this property?
on a little not-so-secret secret...the power of helium. Before we delve into the mechanism of helium
Being the first in a group of elements dubbed the speech, here’s some background information about
noble gases, you’d think that helium would be a helium. Helium was first discovered in 1868, when
dignified sort of element. Indeed, helium is well known scientists were studying the Sun [1]. When light from
for its inertness, a property unique to noble gases, the Sun was resolved into a spectrum, a previously
which is essential for its use in industry. However, helium undocumented line in the spectrum was observed.
can also be used for comic effect: Scientists then pursued this further and proved the
upon inhaling helium, one’s existence of helium in 1895. Denoted by the chemical
voice becomes squeaky and symbol “He”, helium is the second lightest element
seemingly higher pitched. known to humans. Subsequently, helium was found
This phenomenon is called to be very inert, which means it rarely undergoes
“helium speech”. So, I guess chemical reactions with other substances.
I lied; you won’t sound
like Batman, but you will If you’ve heard someone speak after inhaling
sound like a Mickey Mouse helium, you may describe their voice as “squeaky”.
impersonator! You may have 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