Klarinet Archive - Posting 000061.txt from 1996/05

From: Paula Poundstone <hickey@-----.EDU>
Subj: Re: A question about acoustics
Date: Fri, 3 May 1996 19:53:55 -0400

Dan:

Acoustically the clarinet behaves as a cylindrical tube open at one end
with the mouthpiece at the other end. Because a pressure antinode forms
in the mouthpiece it resembles a tube closed at one end and open at the
other. Therefore its fundamental frequency is half that of a tube open at
both ends, and of the same length. This is why a clarinet sounds an
octave lower than a flute even though it is nearly the same length. Since
tubes closed at one end vibrate with modes that are odd multiples of the
fundamental, the next mode of oscillation is three times that of the
fundamental which is a twelfth. This is why the clarinet overblows the
twelfth. If the pressure antinode did not form in the mouthpiece the
clarinet would not behave this way. For example the oboe and bassoon are
also closed at one end but behave differently. They are basically tubes
with conical air columns in which the tip of the cone has been cut off
and the reed attached. A concical air column will vibrate with both even
and odd harmonics, therfore both instruments overblow the octave. The
flute behaves as a tube open at both ends and also overblows the octave.
The saxophone is considered a hybrid because while it overblows the
octave its fingering system is mostly the same as the clarinet. It has a
wide conical bore. I hope this is helpful. I have quoted freely from The
Acoustical Foundations of Music by John Backus. To further understand
nodes and antinodes in the vibrating air column I refer you to chapter
four of the above book. Another good source is Fundamentals of Musical
Acoustics by Arthur H. Benade. These are standard reference books in the
realm of acoustics so they should be easy to find.

Paula Hickey
@-----.edu

If only the birds with the most beautiful voices were to sing the forest
would be silent. Chinese Proverb

On Thu, 2 May 1996, Dan Leeson: LEESON@-----.edu wrote:

> Would some kind soul out there help me understand why the clarinet
> overblows a 12th while a bassoon, a flute, and an oboe overblow an
> octave.
>
> Please, no shooting from the hip, but serious knowledge about the
> phenomenon. Even better would be an explanation followed by a
> scholarly reference.
>
> Much obliged.
>
>
> ====================================
> Dan Leeson, Los Altos, California
> (leeson@-----.edu)
> ====================================
>