Klarinet Archive - Posting 000182.txt from 1996/10

From: Roger Shilcock
Subj: Re: CO2 influencing pitch (fwd)
Date: Tue, 8 Oct 1996 15:29:00 -0400

---------- Forwarded message ----------
Date: Tue, 8 Oct 1996 11:36:24 -0600
From: Steve Prescott <mipresc%RUBY.INDSTATE.EDU@-----.UK>
Subject: Re: CO2 influencing pitch

Enough speculation: (and jokes)

According to Michael J. Moravcsik in his book "Musical Sound", he writes
the following in reference to air and gases: (I'll leave some bits out but
will not do so in such a manner as to change the meaning)

Speed of Sound in Different Media

"....The speed of sound in a given medium also depends on the density of
the material, since the ease of transmitting the oscillation from one
molecule to another can be influenced by how close these molecules are to
each other. The speed also depends on the elasticity properties. In gases
the effect of "elasticity" (corresponding there to pressure) approximately
cancels the effect of density, and so the speed of sound in gases does not
depend very much on density (this proves my speculation wrong). It does
depend, however, on temperature."

The Helium-Filled Singer

Paraphrased: A singer who has inhaled helium will, as we know produce high
squeaky tones. It is important to note that ones vocal cords will work in
the same manner whether we inhale helium or CO2 or N2. According to
Moravcsik, "the vibrational frequencies of the vocal cords depend only on
their own geometrical parameters and on their stiffness." The primary
vibrator (vocal cords) will produce the same mixture of frequencies as
usual. The "resonant vibrator" , being the oral cavity (size) determines
the wavelengths of the standing waves of gas that fills the cavity. Thus,
the wavelenghts and the frequency will be as before when the singer inhaled
the surrounding air. It is the frequencies of the resonant vibrators that
will be given by the speed of sound in a gas, divided by the characteristic
wavelengths of the resonant vibrators. Since the speed of sound is now
three times larger than it was in air, the frequencies will also be three
times larger. The resonant vibrator is the main determinant.

So, someone in this discourse was correct; I, however, was not.

Steve.

Steve Prescott
Instrument Rep.Tech./ Clarinetist
Indiana State University
mipresc@-----.edu
Picking some bones out: wavelength x frequency @-----. So if the speed
in the medium is lower at constant wavelength, then the frequency is
lower, and contrariwise.
Roger Shilcock