A full size orchestra may sometimes be called a "symphony orchestra" or "philharmonic orchestra"; these prefixes do not indicate any difference either to the instrumental content or role of the orchestra, but can be useful to distinguish different orchestras based in the same city (for instance, the London Symphony Orchestra and the London Philharmonic Orchestra). A symphony orchestra will usually have over eighty musicians on its staff, in some cases over a hundred, but the number of musicians used in a performance varies according to the work being played. A leading chamber orchestra might be forty or fifty strong; some are much smaller than that. Orchestras sometimes use freelance musicians to enable them to perform works which require instrumentalists which they do not have on staff; not all orchestras employ a harpist for example.
The typical symphony orchestra consists of four groups of musical instruments:
Between the instrument groups and within each group of instruments, there is a generally accepted hierarchy of leadership. Every instrumental group (or section) has a Principal (or soloist) who is generally responsible for playing solos within and leading the group. The violins are divided into two groups, first violin and second violin, and therefore have two principals. The principal first violin is called the concertmaster (or leader) and is considered the leader of not only the string section, but of the entire orchestra, subordinate only to the Conductor. The principal trombone is considered the leader of the low-brass (trombone, bass-trombone, tuba) section, while the principal trumpet is generally considered the leader of the entire brass section. Similarly, the principal oboe (or sometimes the principal flute) is considered the leader of the entire woodwind section. The french horn, while technically a brass instrument, often acts in the role of both woodwind and brass. Most sections also have an Assistant principal (or Co-principal, or Associate principal), or in the case of the first violins, an Assistant concertmaster, who often plays a tutti part in addition to replacing the principal in his or her absence. A tutti (or section) player generally plays either a unique but non-solo part (in the case of winds, brass and percussion), or in UNISON with a group (in the case of the strings). Where a solo part is called for in a string section, for example in the violins, that part is invariably played by the section leader.
In modern times, the musicians are usually directed by a conductor, although early orchestras did not have one, using instead the concertmaster or the harpsichordist playing the continuo for this role. Some modern orchestras also do without conductors, particularly smaller orchestras and those specialising in historically accurate performances of Baroque music and earlier.
The most frequently performed Repertoire for a Symphony orchestra is Western classical music or Opera. However, orchestras are sometimes used in Popular music.
In the 17th century and early 18th century instrumental groups were taken from all of the available talent. A composer such as Johann Sebastian Bach had control over almost all of the musical resources of a town, where as Handel would hire the best musicians available. This placed a premium on being able to rewrite music for whichever singers or musicians were best suited for a performance - Handel produced different versions of the Messiah oratorio almost every year.
As nobility began to build retreats from towns, they began to hire standing bodies of musicians. Composers such as the young Joseph Haydn would have, then, a fixed body of instrumentalists to work with. At the same time, travelling virtuoso performers would write concerti which featured their skills, and travel from town to town, arranging concerts from whoever was there. The aristocratic orchestras worked together over long periods of time, making it possible for ensemble playing to improve over time.
This change, from civic music making where the composer had some degree of time or control, to smaller court music making and one-off performance, placed a premium on music which was easy to learn, often with little or no rehearsal. The results were changes in musical style and emphasis on new techniques. Mannheim had one of the most famous orchestras of that time, where notated dynamics and phrasing, previously quite rare, became standard (see Mannheim school). It also attended a change in musical style from the complex Counterpoint of the Baroque period, to an emphasis on clear Melody, homophonic textures, short phrases, and frequent cadences: a style which would later be defined as classical.
Throughout the late 18th century composers would continue to have to assemble musicians for a performance, often called an "Academy", which would, naturally, feature their own compositions. In 1781, however, the Leipzig Gewandhaus Orchestra was organized from the merchants concert society, and it began a trend towards the formation of civic orchestras which would accelerate into the 19th century. In 1818, Boston's Handel and Haydn Society was founded, in 1842 the New York Philharmonic and the Vienna Philharmonic were formed, and in 1858, the Hallé Orchestra was formed in Manchester. There had long been standing bodies of musicians around operas, but not for concert music: this situation changed in the early 19th century as part of the increasing emphasis in the composition of symphonies and other purely instrumental forms. This was encouraged by composer critics such as ETA Hoffman who declared that instrumental music was the "purest form" of music. The creation of standing orchestras also resulted in a professional framework where musicians could rehearse and perform the same works over and over again, leading to the concept of a Repertoire in instrumental music.
In the 1830s conductor François Antoine Habeneck, in order to perform the symphonies of Beethoven, which had not been heard in their entirety in Paris, began rehearsing a selected group of musicians. He developed techniques of rehearsing the strings separately, notating specifics of performance, and other techniques of cueing entrances which were spread across Europe. His rival and friend Hector Berlioz would adopt many of these innovations in his touring of Europe.
This was paralleled by a rapid standardization of instruments. The invention of the piston or valve by Stolzel and Blilmel, both Silesians, in 1815, was the first in a series of innovations, including the use of valves for the flute by Theobald Boehm and the innovations of Adolphe Sax in the woodwinds. These advances would lead Hector Berlioz to write his famous book on Instrumentation, which was the first systematic treatise on the use of instrumental sound as an expressive element of music.
The effect of the invention of valves was felt at once: instrument-makers in all countries helped with each other in making use of the newly refined instruments and in bringing them to perfection; and the orchestra was before long enriched by a new family of valved instruments, variously known as tubas, or euphoniums and bombardons, having a chromatic scale and a full sonorous tone of great beauty and immense volume, forming a magnificent bass. This also made possible a more uniform playing of notes or Intonation, which would lead to a more and more "smooth" orchestral sound which would peak in the 1950s with Eugene Ormandy and the Philadelphia Symphony Orchestra and the conducting of Herbert von Karajan.
During the transition to using these instruments, which made the performance of more difficult works easier, many composers, including Wagner and Berlioz, would demand the use of "natural" chromatic stops rather than the use of valves for their compositions. However, over time, use of the valved instruments became standard, indeed universal, until the revival of older instruments in the contemporary movement towards Authentic performance (sometimes known as "historically informed performance").
New orchestral effects were possible now that standing orchestras had been formed, winds and brass had been expanded, and had an increasingly easy time playing in tune with each other: particularly the ability for composers to score for large masses of wind and brass which previously had been impractical. Works such as the Requiem of Berlioz would have been impossible to perform just a few decades earlier, with its demanding parts for twenty woodwinds, as well as a gigantic brass ensemble including six horns, eight trumpets, eight trombones, and three tubas.
The next major expansion of symphonic practice came, ironically, from Wagner's Bayreuth orchestra, founded to play his musical dramas. Wagner needed to have a series of composers and notators for the complex scores which he wrote, and had a specific role for the conductor of an orchestra that he described in his influential work "On Conducting". This led to a revolution in orchestral practice, and set the style for orchestral performance for the next eighty years. Wagner's theories changed tempi, dynamics, bowing of string instruments and the role of principals in the orchestra. Conductors who studied his methods would go on to be influential themselves.
As the early 20th century dawned, symphony orchestras were larger, better funded and better trained than ever before, and consequently composers could compose larger and more ambitious works for them. With the recording era beginning, the standard of performance reached a pinnacle, with many older conductors and composers remembering a time when simply "getting through" the music as best as possible was the standard. Since recordings could "fix" small errors in a particular studio performance, and reach people who would never have been able to travel to distant cities - the ability of listeners to compare performances across decades led to a renewed focus on particular conductors and on a high standard of orchestral execution.
In the 1920s and 1930s economic and artistic considerations led to the formation of small concert societies, particularly those dedicated to the performance of music of the avant-garde, including Igor Stravinsky and Arnold Schoenberg. This tendency to start festival orchestras or dedicated groups would also be pursued in the creation of summer musical festivals, and orchestras for the performance of smaller works. Among the most influential of these was the Academy of St. Martin in the Fields under the baton of Sir Neville Marriner.
With the advent of the early music movement, orchestras where players worked on execution of works in styles derived from the study of older treatises on playing became common. These include the London Classical Players under the direction of Sir Roger Norrington and the Academy of Ancient Music under Christopher Hogwood, among others.
The late 20th century saw a crisis of funding and support for orchestras in the United States and, to a lesser extent, in Europe. The size and cost of a symphony orchestra, compared to the size of the base of supporters, became an issue which struck at the core of the institution. Along with the drastic falling off of revenues from recording, tied to no small extent to changes in the recording industry itself, a period of change began which has yet to reach its conclusion. Critics such as Norman Lebrecht were vocal in their diagnosis of the problem as the "jet set conductor" and the problems of orchestral repertory and management, while other music administrators such as Michael Tilson Thomas and Esa-Pekka Salonen argued that new music, new means of presenting it, and a renewed relationship with the community could revitalize the symphony orchestra.
Some ensembles, such as the Orpheus Ensemble, based in New York City, have had more success, although decisions are likely to be deferred to some sense of leadership within the ensemble (for example, the principal wind and string players).
Others have returned to the tradition of a principal player, usually a violinist, being the artistic director and running rehearsals (such as the Australian Chamber Orchestra).
In some theaters, the orchestra is the area of seats directly in front of the stage (called "primafila" or "platea"); the term more properly applies to the place in a theatre, or concert hall set apart for the musicians.