the bernoulli principle

The Bernoulli Principle states that an increase in the speed of air occurs simultaneously with decreased air pressure.  So, when we blow across the embouchure hole of the flute, the air pressure inside the small space of the riser becomes lower than the air pressure inside the larger space of the flute’s tube and the air pressure of the room.  Thus, because the air pressure in the riser is lower than the air pressure in the tube, air of the tube and the room rushes toward the riser.  The vibration created from this process begins when the air flowing from the tube, strikes the crown of the flute which is right next to the riser. These vibrations reflect off of the crown and travel back down the tube of the flute. The distance between the point of contact at the crown and the nearest opening in the tube (or the tone hole) determines the length of vibration, and thus the fundamental pitch that is created.  To increase the pitch by an octave, the flutist doubles the speed of the air released into or across the riser, thus doubling the speed of air flowing from the tube and dividing the column of vibration in half. This vibratory action occurs simultaneously to the vibration created by the initial contact of the air striking the edge of the riser, which sends vibrations and air in the opposite direction, or toward the end of the flute.  Finding the balance of these contradictory vibrational directions is key to building a vibrant tone that is filled with carrying power.

This is a concept that flutists should seek to understand, because it suggests the importance of drawing the sound up through the flute toward the crown, as opposed to only sending the air down through the flute toward the foot joint.  It is similar to the string players’ debate between “drawing the sound” or “pressing and pulling the sound.”  A basic understanding of the Bernoulli Principle’s impact on flute tone production suggests that drawing the sound allows the flutist to balance vibrations in order to create the most colorful tone.  Pressing the air down the tube of the flute without facilitating this contradictory vibratory motion, impairs the vitality of sound. 

It certainly sounds odd to those of us who have assumed that the air travelling down the tube of the flute was the only factor in creating tone.  But, try it.  When you blow air across the embouchure hole, do it with the intention of creating a low-pressure space within the riser that will, in turn, draw air up the tube toward the crown.  Do this rather than blowing air with the intention of sending air through the flute tube. 

For instance, if low C represents the longest tube of high-pressure air on the flute, then the flutist must create low pressure in the riser very quickly in order to draw the air up through the tube so that it will strike the crown and create vibration.  This means that the flutist must blow a column of air that moves quickly to the outer wall of the riser.  Further, the air for a low note must be a wide column that covers the entire inside wall of the riser.  Because the column of high-pressure air is so long for low notes, reducing the space within the riser that attracts high pressure-air from the tube creates a faster vibrational response.