In the Baroque era, the size and composition of an orchestra were not standardised. There were large differences in size, instrumentation and playing styles—and therefore in orchestral soundscapes and palettes — between the various European regions. The Baroque orchestra ranged from smaller orchestras (or ensembles) with one player per part, to larger-scale orchestras with many players per part. Examples of the smaller variety were Bach's orchestras, for example in Koethen, where he had access to an ensemble of up to 18 players. Examples of large-scale Baroque orchestras would include Corelli's orchestra in Rome which ranged between 35 and 80 players for day-to-day performances, being enlarged to 150 players for special occasions.

In the classical era, the orchestra became more standardized with a small to medium-sized string section and a core wind section consisting of pairs of oboes, flutes, bassoons and horns, sometimes supplemented by percussion and pairs of clarinets and trumpets.

Beethoven's influence

The so-called "standard complement" of doubled winds and brass in the orchestra pioneered in the late 18th century and consolidated during the first half of the 19th century is generally attributed to the forces called for by Beethoven after Haydn and Mozart. Beethoven's instrumentation almost always included paired flutes, oboes, clarinets, bassoons, horns and trumpets. The exceptions are his Symphony No. 4, Violin Concerto, and Piano Concerto No. 4, which each specify a single flute. Beethoven carefully calculated the expansion of this particular timbral "palette" in Symphonies 3, 5, 6, and 9 for an innovative effect. The third horn in the "Eroica" Symphony arrives to provide not only some harmonic flexibility but also the effect of "choral" brass in the Trio movement. Piccolo, contrabassoon, and trombones add to the triumphal finale of his Symphony No. 5. A piccolo and a pair of trombones help deliver the effect of storm and sunshine in the Sixth, also known as the Pastoral Symphony. The Ninthasks for a second pair of horns, for reasons similar to the "Eroica" (four horns has since become standard); Beethoven's use of piccolo, contrabassoon, trombones, and untuned percussion—plus chorus and vocal soloists—in his finale, are his earliest suggestion that the timbral boundaries of the symphony might be expanded. For several decades after his death, symphonic instrumentation was faithful to Beethoven's well-established model, with few exceptions.

Read more: https://en.wikipedia.org/wiki/Orchestra