Triple horns with five valves are also made, usually tuned in F, B ♭, and a descant E ♭ or F. The more common double horn has a fourth, trigger valve, usually operated by the thumb, which routes the air to one set of tubing tuned to F or another tuned to B ♭ which expands the horn range to over four octaves and blends with flutes or clarinets in a woodwind ensemble. Three valves control the flow of air in the single horn, which is tuned to F or less commonly B ♭. The key of a natural horn can be changed by adding different crooks of different lengths. The pitch of any note can easily be raised or lowered by adjusting the hand position in the bell. Pitch may also be controlled by the position of the hand in the bell, in effect reducing the bell's diameter. A horn without valves is known as a natural horn, changing pitch along the natural harmonics of the instrument (similar to a bugle).
The backward-facing orientation of the bell relates to the perceived desirability to create a subdued sound in concert situations, in contrast to the more piercing quality of the trumpet. Most horns have lever-operated rotary valves, but some, especially older horns, use piston valves (similar to a trumpet's) and the Vienna horn uses double-piston valves, or pumpenvalves. Pitch is controlled through the combination of the following factors: speed of air through the instrument (controlled by the player's lungs and thoracic diaphragm) diameter and tension of lip aperture (by the player's lip muscles-the embouchure) in the mouthpiece plus, in a modern horn, the operation of valves by the left hand, which route the air into extra sections of tubing. A musician who plays a horn is known as a horn player or hornist.
THE ART OF FRENCH HORN PLAYING MUTES PROFESSIONAL
The double horn in F/B ♭ (technically a variety of German horn) is the horn most often used by players in professional orchestras and bands. The French horn (since the 1930s known simply as the horn in professional music circles) is a brass instrument made of tubing wrapped into a coil with a flared bell.