• Functional principles of brass instruments

• The function of air in brass instruments
• Air stream and the standing wave
• The analogy between the human voice and brass instruments

The function of air in brass instruments

Air has four different roles in tone production:

1. Compressed air

Before the note starts, the lip aperture is closed by the player’s tongue (like the t-consonant). To be able to start the lip vibration, the player has to increase the air pressure inside his/her lungs and mouth cavity. For soft, low notes a small overpressure is sufficient, but the higher and louder one plays, the more air pressure will be needed to start and maintain the lip vibration.

2. Excitation

After the valve (tongue) has been opened, the air starts to stream through the lip aperture. Provided that the lips are tuned in a suitable way they start vibrating like human vocal cords. Part of the kinetic energy of the air stream excites the vibrator, and the rest continues through the tubing. After passing the lip aperture the air stream no longer plays an essential role in tone production.

3. Standing wave

When the lips vibrate at the proper frequency, the air column inside the instrument will resonate and form a standing wave. This creates a pressure distribution with nodes and antinodes in certain points that depend on the inner geometry of the instrument.

4. Transmitting wave outside the system

When the pressure impulse reaches the bell, one part of it reflects and the other part continues spreading in the free space outside of the instrument. The latter makes the audible sound that travels in every direction as a spherical wave at a speed of 340 m/s.

Printable version