Klarinet Archive - Posting 000197.txt from 1996/10

From: Jonathan Cohler <cohler@-----.NET>
Subj: Re: CO2 influencing pitch
Date: Tue, 8 Oct 1996 18:23:06 -0400

This is not correct. The CO2 content does effect pitch. Here's why.

The thing that is vibrating in a clarinet (besides the reed) is the air
column inside the instrument. Essentially, it is the column of air that
starts at the mouthpiece and continues to the first open hole. Blowing
through the reed excites the air column, and the vibrating air column
sustains the vibration of the reed through appropriate feedback, but it is
the vibrating air column that creates the sound that is then propragated
out in to the larger air space that you refer to.

Therefore the CO2 content of that small volume of the air column is very
relevant. The more CO2 the lower the pitch will be. Because the frequency
of vibration is given by:

f = V / L

Where V is the velocity of sound in the medium and L is the wavelength.
The wavelength is fixed by the dimensions of the instrument, so the
frequency is dependent on the velocity of sound in the medium. Therefore,
with more CO2 in the air column it vibrates at a lower frequency. This
vibration is then transmitted to the surrounding atmosphere.

By the way, this simple formula explains also why clarinets get sharp when
it is hot. And also why a clarinet "warms up". As the average temperature
in the air column of a clarinet rises, the speed of sound increases, and
therefore the frequency goes up.

As for "air support" I'm not really sure what you mean. It's one of those
ambigously defined, virtually meaningless, phrases that clarinetists, and
wind players in general, tend to throw around a lot.

If what you mean is blowing air pressure, then the opposite is true. As
air pressure drops on the clarinet, pitch tends to go up slightly (not
down). I have discussed this in previous posts, but the basic reason is
that the natural overtones on the clarinet are slightly flat from the
perfect 3x, 5x, 7x relationships that they would be in an "ideal" tube.
When one plays soft, the sound is made up almost entirely of fundamental
frequency (close to a pure sign wave). As one gets louder, more and more
of the upper harmonics are added into the sound. Since they are flat from
where they should be, the ear hears the composite sound as being flatter.

As you say, relaxation of the embouchure will also certainly lower the pitch.

----------------------------
Jonathan Cohler
cohler@-----.net

At 9:53 AM 10/8/96, Scott D. Morrow wrote:

>I SAY:
>
> Perhaps I am just unenlightened, but, in the absence of a more
>colourful Dan Leeson characterization, I find this all sounds like a lot of
>nonsense!
> First of all, I have read NOTHING in this discourse that could even
>remotely suggest that any change in pitch could be related to the CO2
>content of the air being forced through the clarinet. Everything I've read
>here - from belching to breath-holding- sounds more like the effect of
>proper air-column support and effective use of the diaphragm (THAT's why
>you'd wait a couple of seconds after taking your breath before attacking)
>on the pitch rather than from the gas mixture in that air in our lungs!
> Secondly, even if sound travels faster or slower in CO2 than in N2,
>it is completely irrelevant because we are not LISTENING to that sound
>travelling through CO2: we are listening to it travelling through AIR
>(N2). So, unless you are a volcano and the amount of air you blow through
>your instrument can drastically affect the air composition in the room
>around you, IT DOESN'T MAKE ANY DIFFERENCE!
> My proposal is:
> The soundwaves emanating from the clarinet are dependent on
>the acoustics of the instrument and the air support used to create the
>tone.
> The composition of that air, alone, does not affect the pitch.
> The pitch MAY be altered by reduced air column support
>caused by ineffective use of the diapragm and breathing techniques (i.e.,
>hyperventilation, etc.) and relaxation of the embouchure due to fatigue or
>loss of control as a result of overriding bodily functions (i.e., belching,
>coughing, smiling, etc.).
> If you drink and play, please make sure you have a
>designated soloist!
>
> -Scott
>
>
>Scott D. Morrow
>Department of Biochemistry
>School of Hygiene and Public Health
>Johns Hopkins University
>(410)-955-3631
>
>SDM@-----.edu

   
     Copyright © Woodwind.Org, Inc. All Rights Reserved    Privacy Policy    Contact charette@woodwind.org