A brass instrument is a musical instrument whose sound is produced by sympathetic vibration of air in a tubular resonator in sympathy with the vibration of the player's lips. Brass instruments are also called labrosones, literally meaning "lip-vibrated instruments".
There are several factors involved in producing different pitches on a brass instrument: One is alteration of the player's lip tension (or "embouchure"), and another is air flow. Also, slides (or valves) are used to change the length of the tubing, thus changing the harmonic series presented by the instrument to the player.
The view of most scholars (see organology) is that the term "brass instrument" should be defined by the way the sound is made, as above, and not by whether the instrument is actually made of brass. Thus, as exceptional cases one finds brass instruments made of wood like the alphorn, the cornett, the serpent and the didgeridoo, while some woodwind instruments are made of brass, like the saxophone.
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Families of brass instruments
Modern brass instruments generally come in one of two families:
Valved brass instruments use a set of valves (typically three or four but as many as seven or more in some cases) operated by the player's fingers that introduce additional tubing, or crooks, into the instrument, changing its overall length. This family includes all of the modern brass instruments except the trombone: the trumpet, horn (also called the French horn), euphonium, and tuba, as well as the cornet, flügelhorn, tenor horn (alto horn), baritone horn, sousaphone, mellophone, and the old saxhorn. As valved instruments are predominant among the brasses today, a more thorough discussion of their workings can be found below. The valves are usually piston valves, but can be rotary valves. Rotary valves are the norm for the horn and are also prevalent on the tuba.
Slide brass instruments use a slide to change the length of tubing. The main instruments in this category are the trombone family, though valve trombones are occasionally used, especially in jazz. The trombone family's ancestor, the sackbut, and the folk instrument bazooka are also in the slide family.
There are two other families that have, in general, become functionally obsolete for practical purposes. Instruments of both types, however, are sometimes used for period-instrument performances of Baroque- or Classical-era pieces. In more modern compositions, they are occasionally used for their intonation or tone color.
Natural brass instruments, on which only notes in the instrument's harmonic series are available. Such instruments include the bugle and older variants of the trumpet and horn. The trumpet was a natural brass instrument prior to about 1795, and the horn before about 1820. In the 18th century different-length interchangeable crooks were developed which enabled a single instrument to be used for more than one key. Natural instruments are still played for period performances and some ceremonial functions, and are occasionally found in more modern scores, such as those by Richard Wagner and Richard Strauss.
Keyed or Fingered brass instruments used holes along the body of the instrument, which were covered by fingers or by finger-operated pads (keys) in a similar way to a woodwind instrument. These included the cornett, serpent, ophicleide, keyed bugle and keyed trumpet. They are more difficult to play than valved instruments.
Bore taper and diameter
Brass instruments may also be characterised by two generalizations about geometry of the bore, that is, the tubing between the mouthpiece and the flaring of the tubing into the bell. Those two generalizations are with regard to
◘ the degree of taper or conicity of the bore and
◘ the diameter of the bore with respect to its length.
Cylindricality vs. conicality
While all modern valved and slide brass instruments consist in part of conical and in part of cylindrical tubing, they are divided as follows:
◘ Cylindrical bore brass instruments are those in which approximately constant diameter tubing predominates. Cylindrical bore brass instruments are generally perceived as having a brighter, more penetrating tone quality compared to conical bore brass instruments. The trumpet, baritone horn and all trombones are cylindrical bore. In particular, the slide design of the trombone necessitates this.
◘ Conical bore brass instruments are those in which tubing of constantly increasing diameter predominates. Conical bore instruments are generally perceived as having a more mellow tone quality than the cylindrical bore brass instruments. The "British brass band" group of instruments fall into this category. This includes the flugelhorn, cornet, tenor horn (alto horn), horn, euphonium and tuba. Some conical bore brass instruments are more conical than others. For example, the flugelhorn differs from the cornet by having a higher percentage of its tubing length conical than does the cornet, in addition to possessing a wider bore than the cornet. In the 1910s and 1920s, the E.A. Couturier company built brass band instruments utilizing a patent for a continuous conical bore without cylindrical portions even for the valves or tuning slide.
Whole-tube vs. half-tube
The second division, that based on bore diameter in relation to the length determines whether it is the fundamental tone or the first overtone which is the lowest partial practically available to the player:
◘ Whole-tube instruments are ones in which the fundamental tone can be played with ease and precision. Their bore is the larger with relation to the length of the tubing. The tuba and the euphonium are instances of whole-tube brass instruments.
◘ Half-tube instruments are ones in which the fundamental tone cannot easily or accurately be played. Their bore is the smaller with relation to the length of the tubing. The second partial (first overtone) is the lowest note of each tubing length practical to play on half-tube instruments. The trumpet and horn are instances of half-tube brass instruments.
