http://en.wikipedia.org/wiki/Euphonium

The euphonium is a conical-bore, tenor-voiced brass instrument. It
derives its name from the Greek word euphonion, meaning
"beautiful-sounding" or "sweet-voiced". The euphonium is a valved
instrument, and nearly all models are piston valved, though German
rotary valved models do exist.
A person who plays euphonium is sometimes called a
euphoniumist.
Contents [hide]
1 Construction and general characteristics
2 Name recognition and misconceptions
3 History and development
4 Performance venues and professional job opportunities
5 College situation
6 Lists of important players
7 Important literature
8 Some famous band pieces with euphonium solos
9 The euphonium in orchestras
10 References
11 External links
[edit]
Construction and general characteristics
The euphonium is pitched in concert B-flat (Bb), meaning that when
no valves are depressed the instrument will produce partials of the
B-flat harmonic series. In the United States, music for the
instrument is usually written in the bass clef at concert pitch
(that is, without transposition), though treble-clef euphonium
parts, transposing down a major ninth, are often included in
school-level concert band music for the sake of students who have
recently switched from the trumpet, or who play trumpet and are
doubling on euphonium. In the brass band tradition, especially in
the United Kingdom, euphonium music is always written this way. In
continental European music, parts for the euphonium are sometimes
written in the bass clef but a major second higher than sounding
pitch.
Current professional models have three top-action valves, played
with the first three fingers of the right hand, plus a
"compensating" fourth valve found midway down the right side of the
instrument, played with the left index finger. Beginner models
often have only the three top-action valves, while some
intermediate "student" models may have a fourth top-action valve,
played with the fourth finger (the "pinky") of the right hand; such
an instrument is shown in the above picture. Compensating systems
are expensive to build, and there is in general a wide discrepancy
between the costs of compensating and non-compensating models. For
a thorough discussion of the valves and the compensation system,
see the article on brass instruments.
The euphonium has an extremely broad functional range compared to
cylindrical-bore instruments; professional players can commonly
produce notes up to F six ledger lines above the bass clef or even
higher, though fourth ledger line Bb is a normal limit for younger
players. On the bottom end, the true (non-pedal) range of
compensating four-valve euphoniums goes down to B-natural below the
bass clef up to in professional hands, though if the fourth valve
is non-compensating the lowest non-pedal tone available is C, a
half-step higher. If the instrument has only three valves, E below
the bass clef is the lowest non-pedal tone possible. On all models,
however, pedal tones, the fundamentals of the instrument's harmonic
series, are comparitively easily produced, and extend the range a
further octave down, almost to the bottom of the piano
keyboard.
As with the other conical-bore instruments, the cornet, flugelhorn,
French horn, and tuba, the euphonium's tubing gradually increases
in diameter throughout its length, resulting in a softer, gentler
tone compared to cylidrical-bore instruments