Clarinet
Use of multiple clarinets

The modern orchestral standard of using soprano clarinets in B ♭ and A has to do partly with the history of the instrument and partly with acoustics, aesthetics, and economics. Before about 1800, due to the lack of airtight pads, practical woodwinds could have only a few keys to control accidentals (notes outside their diatonic home scales). The low (chalumeau) register of the clarinet spans a twelfth (an octave plus a perfect fifth) before overblowing, so the clarinet needs keys/holes to produce all nineteen notes in this range. This involves more keywork than on instruments that "overblow" at the octave— oboes, flutes, bassoons, and saxophones need only twelve notes before overblowing. Since clarinets with few keys cannot play chromatically, they are limited to playing in closely related keys. For example, an eighteenth-century clarinet in C could play music in F, C, and G (and their relative minors) with good intonation, but with progressive difficulty and poorer intonation as the key moved away from this range. With the advent of airtight pads and improved key technology, more keys were added to woodwinds and the need for clarinets in multiple keys was reduced. The use of instruments in C, B ♭, and A persisted, with each used as specified by the composer.

The lower-pitched clarinets sound "mellower" (less bright), and the C clarinet—the highest and brightest sounding of these three—fell out of favor as the other two could cover its range and their sound was considered better. While the clarinet in C began to fall out of general use around 1850, some composers continued to write C parts, e.g., Bizet 's Symphony in C (1855), Tchaikovsky 's Symphony No. 2 (1872), Smetana 's overture to The Bartered Bride (1866) and Má Vlast (1874), Dvořák's Slavonic Dance Op. 46, No. 1 (1878), Brahms ' Symphony No. 4 (1885), Mahler's Symphony No. 6 (1906), and Strauss ' Der Rosenkavalier (1911).

While technical improvements and an equal-tempered scale reduced the need for two clarinets, the technical difficulty of playing in remote keys persisted, and the A has remained a standard orchestral instrument. By the late 19th century the orchestral clarinet repertoire contained so much music for clarinet in A that it has remained in use.
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