The string orchestra consists of instruments belonging to the violin family (violin [two sections], viola, violoncello, double bass) with doubling of each part by anywhere from a few musicians to several. Some string orchestra compositions additionally call for harp and/or piano, but because such a substantial repertoire exists for the string orchestra without these two instruments they will not be treated as basic to the instrumentation of the string orchestra in this essay. One way of thinking about the string orchestra is as an enlarged string quartet with the bass register (violoncello part) fortified an octave below by the addition of the double bass. Indeed, a few noteworthy works in the string orchestra repertoire are arrangements of string quartet works (e.g., Samuel Barber’s Adagio for Strings). But a far larger portion of the repertoire for string orchestra was conceived for a performance force with five sections of stringed instruments. The history of this ensemble combination begins in the Classical Era of the late 18th century soon after the Baroque practice of including basso continuo parts in compositions began to lose favor. Some early symphonies by Mozart, Haydn, and other composers of that era were published for strings only and without basso continuo parts, and these might be considered the earliest works for the string orchestra. Orchestral composers of the late 18th century and the entire 19th century favored orchestra combinations with ever increasing wind and percussion sections in addition to the strings, but in the 20th century a number of composers returned to the string orchestra ideal at least for some of their works. These works are frequently programed on symphony orchestra concert programs, and when performed the orchestra's wind and percussion players are absent, leaving only the string players on stage.
(by Roger Vetter)