بعد البحث وجدت ان المناهج القديمة كانت تحدد البطن والعقدة من خلال إزاحات الجزيئات ...
وفي المناهج الجديدة من خلال التضاغط ..
وهذا الشرح يفرق بين لعقدة والبطن في الأنابيب وآلات النفخ ...
Standing Waves in Wind Instruments
The string disturbs the air molecules around it as it vibrates,
producing sound waves in the air. But another great container for
standing waves actually holds standing waves of air inside a long,
narrow tube. This type of instrument is called an aerophone, and the
most well-known of this type of instrument are often called wind
instruments because, although the instrument itself does vibrate a
little, most of the sound is produced by standing waves in the column of
air inside the instrument.
If it is possible, have a reed player and a brass player demonstrate to
you the sounds that their mouthpieces make without the instrument. This
will be a much "noisier" sound, with lots of extra frequencies in it
that don't sound very musical. But, when you put the mouthpiece on an
instrument shaped like a tube, only some of the sounds the mouthpiece
makes are the right length for the tube. Because of feedback from the
instrument, the only sound waves that the mouthpiece can produce now are
the ones that are just the right length to become standing waves in the
instrument, and the "noise" is refined into a musical tone.
Figure 6: Standing Waves in a wind instrument are usually shown as
displacement waves, with nodes at closed ends where the air cannot move
back-and-forth.
Standing Waves in Wind Instruments
The standing waves in a wind instrument are a little different from a
vibrating string. The wave on a string is a transverse wave, moving the
string back and forth, rather than moving up and down along the string.
But the wave inside a tube, since it is a sound wave already, is a
longitudinal wave; the waves do not go from side to side in the tube.
Instead, they form along the length of the tube.
Figure 7: The standing waves in the tubes are actually longitudinal
sound waves. Here the displacement standing waves in Figure 6 are shown
instead as longitudinal air pressure waves. Each wave would be
oscillating back and forth between the state on the right and the one on
the left. See Standing Waves in Wind Instruments for more explanation.
Longitudinal Waves in Pipes
The harmonics of wind instruments are also a little more complicated,
since there are two basic shapes (cylindrical and conical) that are
useful for wind instruments, and they have different properties. The
standing-wave tube of a wind instrument also may be open at both ends,
or it may be closed at one end (for a mouthpiece, for example), and this
also affects the instrument. Please see Standing Waves in Wind
Instruments if you want more information on that subject. For the
purposes of understanding music theory, however, the important thing
about standing waves in winds is this: the harmonic series they produce
is essentially the same as the harmonic series on a string. In other
words, the second harmonic is still half the length of the fundamental,
the third harmonic is one third the length, and so on. (Actually, for
reasons explained in Standing Waves in Wind Instruments, some harmonics
are "missing" in some wind instruments, but this mainly affects the
timbre and some aspects of playing the instrument. It does not affect
the basic relationships in the harmonic series