The French horn (so called to distinguish it from the English horn, a member of the oboe family) is the developed European orchestral member of the true horn family. The instrument is classified technically as a lip-vibrated aerophone , characterized by a conical bore and funnel-shaped mouthpiece, as opposed to the cylindrical bore and cup-shaped mouthpiece of the trumpet family.
Descended from primitive animal-horn prototypes (for example, the biblical shofar), short, curved horns were used in medieval Europe primarily as signal instruments, especially for the hunt; they could usually be relied on only for the rhythmic sounding of a single pitch. In the late 16th and 17th centuries the horn, from this time usually made of brass, was lengthened and coiled--first in a small, spiral coil, later in a wider, open loop. By the late 17th century in France the cor de chasse ("hunting horn") emerged with a wide, flaring bell and a tube length of up to 4.37 m (14 ft), the obvious prototype of the modern instrument. Responsive to a greatly increased number of its natural overtones , the cor de chasse possessed a wide enough range of pitches for use in the orchestra of the early 18th century.
The addition of "crooks" (curved extensions to the tubing of various lengths) and the technique--attributed to the Dresden virtuoso Anton Joseph Hampel--of altering the pitch by stopping the bell with the hand made the horn still more complete melodically in its middle ranges, thus greatly increasing its versatility in the orchestra of the classical period of Haydn and Mozart. Also at this time (the late 18th century) the cup-shaped, trumpetlike mouthpiece was abandoned for the funnel-shaped mouthpiece of the modern horn, resulting in a smoother, less raucous sound.
During the early 19th century valves were added (patented in 1818 by Heinrich Stolzel and Friedrich Bluhmel in Berlin) to vary the playing length of the tube, yielding an instrument virtually chromatic (proceeding by semitones) throughout its range. Although it was slow to be accepted, the valve horn prevailed by the end of the 19th century. The modern French horn is usually pitched in F, and has three valves and a tube length of about 3.75 m (12 ft). The great demands on the resources of the horn have led to the widespread adoption of the "double horn," in which a separate set of coils for a horn in B-flat is added to a horn in F, a fourth valve acting as a switch between the two sets of coils.