Tone Production in Wind Instruments

Musical wind instruments, or aerophones, produce tones by vibrating an enclosed column of air. The two main types of wind instruments are woodwinds (such as flutes, oboes, clarinets, and bassoons) and brass instruments (such as trumpets, French horns, trombones, and tubas).

All these instruments produce their fundamental tones and their natural series of tones in much the same way.

Pitch and Tone Color of a Pipe
Neither the material, such as wood or brass, nor the shape, such as straight or bent, of the pipe has any effect on the pitch or the tone color of the sound produced by the pipe, or tube, of a wind instrument.

The pitch of the vibrations produced by a wind instrument depends on the length of the pipe and on whether the pipe is open or closed.

The tone color, or timbre (i.e., the distinctive quality distinguishing the sound of one instrument from that of another) depends on a wider range of factors, such as the type of mouthpiece, the cylindrical or conical shape of the bore, and the widening of the bell at the end of the instrument.

Harmonics of a Pipe
A pipe of a given length will produce only one tone, called the fundamental tone or the pedal tone. However, by careful manipulation of their breath and lips, players can also produce, by a technique called overblowing, a pipe's higher harmonics, or overtones, the soft tones that accompany the fundamental and, through their relative intensities, give the instrument its individual tone color. These tones are the natural tones of a wind instrument.

Whole-tube instruments are those in which the air column can fairly easily be made to vibrate as a whole and thereby produce the fundamental. In this category are all the woodwinds as well as the large-bore brass instruments, i.e., the tubas.

Half-tube instruments are those in which the air column has a strong tendency, even with the slightest air pressure, to vibrate at the half length and thereby produce the harmonic just above the fundamental rather than the fundamental itself. In this category are the narrow-bore brass instruments, such as the trumpets, French horns, and trombones. However, on modern trumpets, most skilled players can now produce the fundamental.

Open Pipes and Stopped Pipes
Open pipes are those that are open at their lower end. Most wind instruments are open pipes, and the above description applies to them.

An open pipe is said to "overblow at the octave" because it is capable of playing the instrument's second harmonic, the octave (the first harmonic being the fundamental).

Stopped pipes are those that are closed at their lower end. A stopped pipe of the same length as an open pipe has a fundamental that is an octave lower than that of the open pipe.

A stopped pipe can play only the odd-numbered harmonics above its fundamental. Therefore, a stopped pipe is said to "overblow at the fifth" because the first harmonic it can play above the fundamental is the third harmonic, which is the interval of a twelfth (an octave plus a fifth).

The most common place to find musical stopped pipes is on an organ, where they are used to produce low tones with short pipes.

Nearly all the woodwinds and brass instruments produce their basic tones as open pipes. Such instruments function the same way because they all have bores that are conical (larger at one end than at the other), one end that is closed by the mouthpiece, and the other end that is open. The exception is the flute, which is mostly cylindrical, but its open embouchure (giving it openings at both ends) makes it function as an open pipe.

However, one important woodwind acts as a stopped pipe-the clarinet. The reason for its behavior is that it is a cylindrical tube closed at one end by the mouthpiece. Such a tube tends to act the same way as a stopped pipe even though it is not actually stopped at the lower end. Therefore, the clarinet has a fundamental that is an octave lower than a similar tube length would produce in an open pipe. And the clarinet will "overblow at the fifth."

Filling in the Gaps
The above techniques will give each instrument a basic matrix of pitches-its fundamental and its available natural tones. Filling in the gaps between the natural series is the function of a complex set of attached devices, differing by instrument, such as slides, crooks, valves, and side holes.
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The New Grove Dictionary of Music and Musicians. 2nd ed. London: Macmillan, 2001.