Back pressure in the flute and the mouth cavity
Visualizations can be useful in developing embouchure and sound production, but what is actually happening in the breath/flute relationship when a sound is made?
First of all the lungs are pressurized by an in-breath, then the mouth/throat cavity is allowed to fill and pressurize against the narrow embouchure opening between the lips.
As we release air into the flute, the flute becomes pressurized and exerts a back pressure against the embouchure opening and thus the lungs and mouth cavity. So really, there are two pressurized cavities joined in the middle by a narrow opening: the lips. As you become more efficient with pressurizing the flute, you become aware of the quality of the back pressure from the flute and the quality of the opposing pressure in the mouth/throat cavity. Beginner players generally have a ‘loose’ embouchure with which it is difficult to create either the mouth cavity pressure or the pressure in the flute. By fine-tuning the embouchure opening and feeling the pressure changes in the two chambers, a player can gauge and craft the efficiency of their tone making.