Klarinet Archive - Posting 000046.txt from 2010/08
From: Diego Casadei <casadei.diego@-----.com>
Subj: [kl] Fundamental error on
Date: Thu, 12 Aug 2010 03:22:38 -0400
Dear all,
there is one big mistake on
http://www.woodwindcourse.co.uk/user/image/clarinet_bore_design.doc
which is worthwhile explaining here (few other details have been already
commented by other people).
In every wind instrument (*) the sound generator is just at the edge of
the pipe which is controlled by the mouth. In particular, for the reed
instruments the sound generator is the vibrating reed (or reeds for
double-reed winds). This means that the clarinet reed exerts the
pressure with the maximum amplitude on the column of air which is
resonating inside the pipe.
In diagrams like the drawing on page 4 of the document mentioned above,
a "node" is a position along the tube in which the amplitude is minimum
(ideally, it is null). The paper calls "antinode" a position which
senses the maximum amplitude (**). Hence, the diagram on page 4 is
clearly wrong: a node is not allowed at the reed position, because that
is by definition the only certain place in which the amplitude is maximum.
The clarinet has one antinode at the reed and one just at the exit from
the bell. They are always there for all pitches. If I remember
correctly, there is also a node in a fix position quite near the
mouthpiece, in the barrel (perhaps at the end of the mouthpiece?) which
is a characteristic of the clarinet, hence the diagram on page 4 of the
mentioned document should be translated a bit to the right and an
antinode should be added to its left, in correspondence with the reed.
For people who master a bit of math, the suggested reading is "The
Physics of Musical Instruments" by N.H.Fletcher and T.D.Rossing
(Springer). An interesting web site (which I had no time to read
through carefully enough) is
http://userpages.umbc.edu/~emrich/clarinet21.html
Cheers,
Diego
(*) Apart from the organ pipes and the flutes, which have the sound
generator where the "cut" is (not exactly at one edge of the pipe).
(**) Whereas the nodes have a fixed position, the position of one
antinode depends on the harmonic under consideration.
--
Diego Casadei
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