The Importance of the Slow Air Chamber in the Native American Flute
The Native American style flute is technically called a ‘dual chambered duct flute’. The flute has two separate hollow chambers separated by an area of solid wood. The chamber closest to the mouth end of the flute is called the slow air chamber. The chamber that terminates on the lower end of the flute is called the barrel or sound chamber of the flute.
This configuration is unique to the Indian or Love flute also called the Native American flute. The two chambers are generally considered to derive from the primitive flute made out of river cane by the Southern Arizona Indian tribes. River cane, like bamboo, is divided into sections by nodes. These Indian flutes use the natural node in the cane too create two chambers.
‘Slow air chamber’ is a sort of misnomer. This chamber got its name from the fact that air moving through this part of the flute is moving slowly in comparison to the air going through the duct of the flute. The air when it funnels into and moves through the constricted duct is going quite fast. It is curious to note that the air moving through the barrel of the flute is actually moving at a much slower speed than the air in the so called slow air chamber.
It is commonly assumed that the slow air chamber is not a very important part of the Native American flute. It’s just sort of there containing the air before the real work of sound generation begins. In my experience this is definitely not the case.
One of the primary characteristics of the tonal quality of a well-constructed Indian flute is its purity. This is in part due to the nature of the stream of air that is striking the splitting edge. The stream of air going through the duct is smooth with little turbulence in it. The air is behaving in this manner because in its journey through the slow air chamber the initial turbulence that is present when it leaves the players mouth and enters the SAC has been largely eliminated. So the SAC acts as a damper of sorts to calm turbulent air.
So a direct, smooth, unimpeded path for the air to follow through the SAC and into the flue are important for a clean, sweet sound. That is why a long, gentle ramp out of the SAC is also important.
The Slow Air Chamber also acts as a secondary resonance chamber. A resonance chamber is a partially enclose space the forces the resonating sound frequencies to bounce back and forth off the wall of the chamber before exiting the chamber space. It is important that the walls of the chamber be smooth and hard and that the space be as large as possible for maximum effect. The bore of the flute is also a resonance chamber. It is not, as some assume, a resonator like the body of an acoustic guitar.
It is generally agreed that a hard wood resonance chamber is more effective than one made of softer material. In the old days speaker boxes were made of hard, dense plywood for this reason.