the exact centre of the tone hole is the nodal point at which the sound wave bounces
As I said in an earlier post,
this is complete nonsense. I am on record as saying, "whenever someone mentions nodes and resonance" speaking about saxophones you should put your hand on your wallet and back slowly out of the room. In almost every instance those who don't know what they are talking about use the term
node when they really mean anti node.
There are two types of nodes present in standing waves: pressure and motion. At a pressure
node there is no change in the pressure of air molecules. At a displacement
node there is no change in motion of the air molecules.
There are also two types of
anti nodes. At a pressure
anti node there is a maximum increase in pressure of air molecules. At a motion
anti node there is a maximum increase in motion of air molecules.
The illustration on the right of a conical shaped bore represents a saxophone. The first is the fundamental, the second one down is the first overtone, the third is the third overtone, and the fourth one down is the fourth overtone. Every note played on a saxophone has these harmonics
and many more. It is easy to visualize how many
nodes and anti nodes are present. Now imagine if every closed tonehole had a
node at its exact center or an
anti node which would make more sense since the pressure or motion would be at its greatest. Think of how many different frequencies (notes) are present when a saxophone is being played and the large number of harmonics of each frequency.
There are instances where there is a pressure
anti node in the vicinity of a tonehole where a leak in a pad has a greater effect upon how a note responds, and if played loud enough can "blow open" a spring closed pad with a weak spring.
This moving animation gives a representation of what is happening with air molecules in a sound wave.
Standing Sound Waves