The musical instrument called a French horn is commonly about 12 to 13 feet (about 3.7 to 4.0 meters) of brass tubing wound into a compact coil. There are several different types, varying primarily by total tubing length and by the number of fingered valves which can change the flow of air through it. Its extreme length translates to the very wide tonal range of a French horn, most being capable of nearly four full octaves of the musical scale. There are, however, limitations and considerations relating to the practical playability of this range.
The earliest, ancient design, called a hunting or natural horn, is still in use as a novelty instrument. Like a simple bugle, its technical range is just one single note. Only a few additional harmonic tones can be created by the musician with techniques such as varying the pursed aperture of the lips, and muting its flared bell opening with the free hand. It has no valves. Its tube length is fixed.
Modern French horns are built with valves. Some instruments, such as the so-called mellophone popular with marching bands, employ simple piston valves similar to those on a trumpet. The unique Vienna horn has a complex double piston system operated by depressing long pushrods. Most French horns in an orchestra are built with rotary valves attached to short levers, operating similarly to stopcock plumbing faucets. The function of valves is to vary the route of air through the instrument, effectively changing its length in increments, which enables the fully chromatic gradations of pitch within the range of a French horn.
Disregarding its valves, the tubular length of a French horn is fixed. It is factory-made to the key of F, or the less popular B-flat model. With three control valves, the basic range of a French horn is from the bass F note three octaves below Middle C to the alto F note one octave above. Some types of horns are made to accept an attachment called crooks — extra lengths of brass tubing — to change its factory-tuned key. The device effectively extends the range of a French horn.
The most commonly used professional French horn is a design called the double horn. It incorporates a fourth valve that routes the flow of air either through one set of tubes tuned to F, or another set tuned to B-flat. Triple horns with yet another valve further stretch the instrument's tonal range to second highest register among the family of brass instruments.
The valves alone cannot create all the potential notes capable of the French horn. The limited combinations of three valves mainly produce the harmonic overtones of the instrument’s defined key. The other notes in between them must still be created by the horn player, sometimes called a hornist, with breath control and precise lip tension. This fundamental technique is called embouchure. Skilled players can exceed the normal range of a French horn and can create midtones subtly off-key of standard musical notes.