Anyone who has ever attended a symphony has probably noted the large number of musicians performing on stage. Dominated by the musicians playing strings, an orchestra is a large grouping of musicians who must manage to play together despite their size. While there is no fixed number at which an orchestra is complete, there are common features to every orchestra and a set number of sections.
There is no set number of instruments that make up a "full" orchestra. In fact, the term itself is misleading and not commonly used in music circles. Instead, the size of an orchestra is often determined by what kind of orchestra it is. Chamber orchestras, for example, are generally smaller than a symphony or philharmonic orchestra, with around fifty musicians performing in a chamber and around one hundred musicians for a philharmonic. It is therefore possible to have a "full" chamber orchestra that would have fewer instruments than a "full" symphony orchestra. There are a number of factors that go into the composition of an orchestra, but in general an orchestra can be considered complete when it has the standard sections, regardless of the number of individual instruments.
A standard orchestra generally has four sections: woodwinds, brass, percussion and strings. There may also be a piano, which is sometimes included as a keyboard section, though generally there is just one piano with an orchestra. Woodwinds are the instruments such as the reed instruments such as the bassoons, oboes and clarinets, and also the flutes and piccolos. Brass instruments are the horns, such as the trumpets, trombones and French horns. Percussion instruments are the drums, the timpani, the cymbals and other similar instruments. The string instruments are the violins, the cellos and the other members of the string family such as the bass and violas. The instruments are usually grouped together in their sections, usually in proportion to one another.
Of the individual instruments, by far the most represented in terms of numbers are the strings. The violins alone frequently outnumber the entire brass section. There may be over thirty violins between the first and second violins--orchestral pieces are often arranged for two different violin parts, hence a first and second violin, with the first violins having the generally more difficult music. By contrast, the entire brass section--the horns, trumpets, trombones and tubas--may only have around fifteen musicians. It should be noted that not all the musicians in an orchestra will play on any given night, as various members of the orchestra may rotate between performances.
The composition of the orchestra often depends on the piece being played. Some pieces, such as Beethoven's "Ode to Joy" for example, require the addition of a choir to the orchestral ensemble. Usually the choir will be placed behind the orchestra. The various sections of the orchestra may also perform as separate ensembles, for example, a string ensemble or a brass ensemble. Specific combinations may also be part of the composer's instructions for the piece. One of Beethoven's compositions, for example, specifies the presence of a single flute.
In addition to the needs of the piece being played, there are a number of other factors that may go into determining how many instruments are included in the full orchestra. For example, when the New York City Philharmonic Orchestra performed in North Korea, they opted to leave behind the piano because it was too large and unwieldy an instrument to properly transport. The location where the orchestra performs also has an impact on the number of instruments. A smaller space means a smaller number of instruments, and may also affect the placement of the sections of the orchestra.