The Structure of the Flute
How is the sound produced?
The flute produces a sound as follows:
First, it is the head joint that produces the sound.
There is an embouchure hole in the lip plate. Place your lower lip so that it covers roughly the lower third of the embouchure hole (with your mouth centered left to right) and, with a slight smile, breath out towards the edge of the hole-the edge being the opposite side of the embouchure hole. Adjust the orientation of the head joint until you find the exact position in which you can produce a sound.
Why does it make a sound?
The principle is the same as that for the recorder. However, on the flute the lips fix the outlet for the breath, while on the recorder the windway fixes the outlet for the breath As the breath is directed toward the edge of the embouchure hole, high-pressure sound waves pass through the tube and reach openings such as the end of the foot joint and the sound holes. These waves then bounce back and try to force the air in the vicinity of the embouchure hole back out through the embouchure hole. As this happens, the sound pressure in this section of the instrument falls, and air is sucked back in. Waves are then produced that cause the air around the edge of the embouchure hole to vibrate up and down, producing changes in the sound.
What happens inside the head joint?
A reflective plate and natural cork are situated to the left of the embouchure hole. We will show this on an acrylic flute built for research purposes.
The reflective plate is fixed in a position 17 mm from the center of the embouchure hole. Under normal circumstances, do not turn the crown (head screw), as this will cause the reflective plate to slip out of place. Breath injected into the flute strikes the reflective plate and is directed to the right. The quality of the cork influences the quality of the sound.
The head joint is not perfectly cylindrical in shape
The head joint tube narrows toward its left end. This is described as a tapered tube. In musical instrument terminology, "tapering" refers to the manner in which a tube opens out. Yamaha manufactures three different types of tapered tube.
A G-tapered tube essentially expands evenly in diameter from the thin end to the thick end. It offers a strong resistance when blown and produces a deep sound. A C-tapered tube has a streamlined shape like a liquor bottle. It is easy to blow into and produces a light timbre. The shape of a Y-tapered tube is a combination of the G- and C-tapered tube shapes, offering moderate resistance when blown and producing a delicate sound.
There are also various types of embouchure hole cuts
There are also a number of variations to the cut of the embouchure hole. First, the embouchure hole can be cut square or rounded, and there can be variation in the amount of shoulder cut or undercut. The nature of the tapering determines the most suitable cut for the embouchure hole, which, in turn, greatly affects the feel of the instrument when you play it.
The distance between the embouchure hole and cork is 17mm
The embouchure hole of a flute is always situated at a distance of 17mm from the cork (more precisely, the near end of the reflective plate.) This is to correct the tuning of each octave, and especially in the third octave.
Because the flute is constructed with two open ends, the length of the tube as calculated based on resonance frequencies is slightly longer than the actual length of the tube. This is called open pipe end correction. Because the length required for this correction grows as the pitch played gets higher, if the flute were a perfect cylinder, as the player goes up the octaves, the intervals between notes would get smaller. This placement of the embouchure hole at a distance of 17mm from the end of the pipe, and the conical shape of the head joint are the solution for providing this pitch interval correction.
This distance and shape is based on the measurements arrived at through a long process of trial and error undertaken by the German instrument maker Theobald Boehm in the 19th century.
The role of the split E mechanism
Not all flutes have a split E mechanism, but on those that do, it is easier to produce an E in the third (top) octave.
When playing this top E, a player releases their left ring finger. If you look at the air oscillation waveform when this happens, you can see that an antinode (where the oscillation is greatest) is located at the left ring finger key.
For action without a split E mechanism, when the left ring finger is released, the key next to it (from the player's perspective, just to the right of the ring finger) opens along with it. Because of this, it is harder to fix the antinode of the wave, making it harder to produce the top E.
Instruments that feature a split E mechanism avoid this situation using this construction that automatically closes the key immediately to the right of the left ring finger when fingering an E. This makes it easier to fix the antinode of the wave, and therefore easier to produce the top E.