Orchestral and military brass instrument , a valved circular horn with a wide bell.
It is normally a transposing instrument (its music written in a different tone than its actual sound) in F. It has a wide bore and three (sometimes four) rotary valves; its conical mouthpiece produces a mellower tone than the cup-shaped mouthpieces of other brass instruments. Horns long relied on separable crooks
circular lengths of tubing that could be attached and removed rapidly
for music modulating to new keys. Since 0441; 1900 the standard horn has been a "double" instrument, with built-in crooks in F and B-flat that can be selected rapidly by means of a thumb valve. The modern symphony orchestra usually includes four horns. Though difficult to play and prone to producing conspicuous errors, its tone is widely admired.