A jazz band (or jazz ensemble) is a musical ensemble that plays jazz music usually without a conductor. Jazz bands usually consist of a rhythm section and a horn section. During the jazz and swing eras in the mid-twentieth century, the most successful jazz orchestras also employed strings and harp in expanded arrangements, but their presence on the bandstand was more for visual impact and not as a key component of the ensemble, although the unique timbres of the strings and harp combined with the band as a whole provided an extra layer of ear-pleasing sonorities.
The rhythm section of a jazz band consists of the percussion, double bass or bass guitar, and usually at least one instrument capable of playing chords, such as a piano, guitar, Hammond organ or vibes. most will usually have more than one of those. Large early jazz bands such as Paul Whiteman’s employed two pianos, an accordion and banjo. The rhythm section is the foundation for the band; it sets the feel for the piece.
The horn section consists of wind and brass instruments, which play the melody and main accompaniment. Typical horns found in a big jazz band include 4 to 5 trumpets, saxophones (2-3 altos, 2 tenors, and a baritone), 3-4 trombones, and a bass trombone. The saxophones may also double on flute, clarinet, bass clarinet and soprano saxophone, the trumpets on flugel horn, and the bass trombone on tuba.