Helium talking

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From: Bill Taylor (bt4_1284@yahoo.com)
Date: Sat Jan 17 2004 - 12:37:15 PST 

Message-ID: <20040117203715.6543.qmail@web40404.mail.yahoo.com>
Date: Sat, 17 Jan 2004 12:37:15 -0800 (PST)
From: Bill Taylor <bt4_1284@yahoo.com>
Subject: Helium talking

Paul:

Do you know where one could get easy access to helium so I can change my
voice as a demo for sound?

Is it safe to do?

Bill

From: Paul Doherty <pauld@exploratorium.edu>

Hi Irene

Helium molecules are less massive than nitrogen and so the speed of sound
in helium is faster than the speed of sound in air. (Helium is 4 amu while

nitrogen is 28 and the average of air is 29 amu) The speed of sound is
proportional to the square root of the molecular mass so the speed of
sound
in helium is (29/4)^0.5 times greater than that in air = 2.7 times
greater.

The resonance frequency of your mouth depends on the time it takes sound
to
cross your mouth cavity. When you fill your mouth with helium the time it
takes sound to cross your mouth (at the high sound speed in helium) is
less
than the time it takes when your mouth is full of air. By 1/2.7.

The resonant frequency of your mouth goes up like the inverse of the
crossing time, it goes up by a factor of 2.7.

So your voice goes up by more than an octave.

The increase in frequency has nothing to do with changing the vibration
frequency of your vocal chords. This is a standard science urban legend.

Paul d

>I was wondering if anyone can give me any information on what causes your

>voice to sound squeeky when you "talk" using the helium gas. Irene
>Hirota
>

=====
Bill Taylor
Drew School
San Francisco
415 661 9667

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