Understanding Wind Instruments
The sound and pitch of a wind instrument is directly related to length and other characteristics. These physical properties dictate the location of the harmonics of the instrument as well as its overall sound.
May 26, 2006
To teach you about wind instrument harmonics we first will use a string instrument to demonstrate some things. Imagine a guitar, violin, or similar string instrument. When a string is plucked or strummed it vibrates along its entire length and produces a specific note that we call the fundamental. The speed and frequency of this vibration is directly related to its composition, its length, and how tightly it is tensioned. The string is also vibrating in subsections of one half its length, one quarter its length, one third of its length, and so on. Each one of these subsections is creating smaller, very faint notes that are proportional to its own shorter length. These faint notes are called overtones or harmonics.
On a string instrument you change the fundamental and its harmonics by shortening or lengthening the length of the overall string. This allows you to get whatever note you choose. On wind instruments instead of a vibrating string, a vibrating column of air is what creates the desired pitch. The shorter the tube of the instrument the shorter the vibrating column of air will be and thus the higher the instrument will play (think of the flute). Likewise the longer the tube is the lower it will play (think of the tuba). Without a mechanism for changing the length of this tube however, the instrument can only play a few widely separated notes by using the harmonics of that specific fundamental tone.
Beginning hundreds of years ago advancements in the construction of instruments began to make it easy to play any note that was required. The addition of valves or keys to an instrument gives the instrument the ability to hit a different fundamental and harmonics. By adding a valve to a trumpet, for example, you can increase the combined length of the tubes (original tube plus the tube connected to the valve). This new length gives the player a new fundamental note and likewise a new set of harmonics above it. Most brass instruments have either three or four valves of various lengths. Woodwind instruments are more complicated with sometimes as many as two dozen or more keys from which to choose. Specific combinations of these keys make the length of the tube the appropriate size for the note the performer is seeking.
For more information about harmonics and the physics behind wind instruments check out my other article on a related topic: Instrument Tuning
