Description and timbre
The pear-shaped bell of the cor anglais gives it a more covered timbre than the oboe, closer in tonal quality to the oboe d'amore. Whereas the oboe is the soprano instrument of the oboe family, the cor anglais is generally regarded as the tenor member of the family, and the oboe d'amore—pitched between the two in the key of A—as the alto member. The cor anglais is perceived to have a more mellow and plaintive tone than the oboe. Its appearance differs from the oboe in that the reed is attached to a slightly bent metal tube called the bocal, or crook, and the bell has a bulbous shape. It is also much longer.
The cor anglais is usually notated in the treble clef, a perfect fifth higher than sounding. Some composers notated it in the bass clef, when the lower register was persistently used, and historically several other options were employed. Alto clef written at sounding pitch is occasionally used, even by as late a composer as Sergei Prokofiev. In late-18th- and early-19th-century Italy, where the instrument was often played by bassoonists instead of oboists, it was notated in the bass clef an octave below sounding pitch (as found in Rossini's Overture to William Tell). French operatic composers up to Fromental Halévy notated the instrument at sounding pitch in the mezzo-soprano clef, which enabled the player to read the part as if it were in the treble clef.
Although the instrument usually descends only to (written) low B♮, continental instruments with an extension to low B♭ (sounding E♭) have existed since early in the 19th century. Examples of works requiring this note (while acknowledging its exceptional nature) include Arnold Schoenberg's Gurre-Lieder, Gustav Mahler's Das Lied von der Erde, Heitor Villa-Lobos's Chôros No. 6, and Karlheinz Stockhausen's Zeitmaße. Antonín Dvořák, in his Scherzo Capriccioso, even writes for the cor anglais down to low A, though it seems unlikely that such an extension ever existed.
Reeds used to play the cor anglais are similar to those used for an oboe, consisting of a piece of cane folded in two. While the cane on an oboe reed is mounted on a small metal tube (the staple) partially covered in cork, there is no such cork on a cor anglais reed, which fits directly on the bocal. The cane part of the reed is wider and longer than that of the oboe. Unlike American style oboe reeds, cor anglais reeds typically have wire at the base, approximately 5 mm (0.20 in) from the top of the string used to attach the cane to the staple. This wire serves to hold the two blades of cane together and stabilize tone and pitch.
Perhaps the best-known makers of modern cors anglais are the French firms of F. Lorée, Marigaux and Rigoutat, the British firm of T. W. Howarth, and the American firm Fox Products. Instruments from smaller makers, such as A. Laubin, are also sought after. Instruments are usually made from African blackwood (aka Grenadilla), although some makers offer instruments in a choice of alternative woods as well, such as cocobolo (Howarth) or violet wood (Lorée), which are said to alter the voice of the cor anglais slightly, reputedly making it even more mellow and warmer. Fox has recently made some instruments in plastic resin and in maple.