Air through the body of the whistle
Looking at a cross section again, we are seeing a circular motion of air in the chamber. It seems as though the air blown into the mouth piece is about to enter the body, but some of it returns, makes one or more saltos and only then enters the body.
In the design of the chamber, I tried to introduce a few optimizations; the bottom and the walls of the chamber are rounded (fillet-ed) , causing the air to tumble and eventually enter the body. I have seen that without these optimizations, the air was less directed and made sharp angles bouncing from the walls.
Now let’s see what happens around a tone hole when air passes through:
We are seeing clearly that the air is drawn to a tone hole, then drops and is drawn to the next tone hole.
Basics of a flute
The air stream, caused by a musician blowing into the mouth piece moves ove the blade. As we have seen earlier, air starts to oscillate; the air stream is distorted. This in turn results in the mouth piece to produce sound; an acoustic wave makes its way through the tube.
The speed a t which this wave moves is about half of the speed at which the air is blown into the entry speed at the beginning of the wind-way. In order to produce a low sounding note, the musician blows gently into the mouth piece. The travel speed of the acoustic wave through the body is low, as the notes produces are low in frequency. To play high notes, the time at which the acoustic wave travels through the body must increase; it requires the air to move faster, and this is done by blowing harder into the mouth piece.
Another interesting thin we are seeing is that at each tone hole, again the air is oscillating, caused by the sharp edge of the tone hole. This is more or less the same what we saw happening at the mouth piece blade; the part of the air that stays inside causes oscillation, which in its turn causes the different acoustic waves. The air oscillates over the entire length of the tube and the locations of the (closed and open) tone holes change this oscillation, thus the acoustic waves. This is what is causing different sounding notes.
From doing some basic simulations, we can see everything functions as it should – in theory. I realize I haven’t explained everything in depth, and what I also did not cover extensively is comparing different shapes and features while doing simulations. True, I have only shown you the end results, but I did uncover some of the unique features we added to this mouth piece…
These new features seem to work. Next is to make sure we have a prototype!
To get our hands on this prototype, we are going to print our design with our trusty 3D printer. Sounds cool, right? Of course, it’s very nice to immediately be able to create a prototype. However, there are some downsides to 3D-printing. We’ll discuss this in part IV, so stay tuned!