A musical ensemble is a group of two or more musicians who perform instrumental or vocal music. In each musical style different norms have developed for the sizes and composition of different ensembles, and for the repertoire of songs or musical works that these ensembles perform.
A group of two musicians is called a duo, a group of three is a trio, a group of four a quartet, and a group of five a quintet. A musician who usually performs alone is usually termed a solo musician or solo artist.
In classical music, trios or quartets either blend the sounds of musical instrument families (such as piano, strings, and wind instruments) or group together instruments from the same instrument family, such as string ensembles or wind ensembles. In jazz ensembles, the instruments typically include wind instruments (one or more saxophones, trumpets, etc.), one or two chordal "comping" instruments (electric guitar, piano, or organ), a bass instrument (electric bass guitar or double bass), and a drummer or percussionist. In rock ensembles, usually called rock bands, there are usually guitars and keyboards (piano, electric piano, Hammond organ, synthesizer, etc.) and a rhythm section made up of a bass guitar and drum kit.
In Western Art music, commonly referred to as classical music, smaller ensembles are called chamber music ensembles. The terms duet, trio, quartet, quintet, sextet, septet, octet, nonet and dectet are used to describe groups of two, three, four, five, six, seven, eight, nine and ten musicians, respectively. A group of eleven musicians, such as found in The Carnival of the Animals, is called either a "hendectet" or an "undectet" (see Latin numerical prefixes). A solo is not an ensemble because it only contains one musician.
The four-piece band is the most common configuration in rock and pop music. Before the development of the electronic keyboard, the configuration was typically two guitarists (one lead guitarist and one rhythm guitarist, with the latter on vocals), a bassist (typically the electric bass guitar) and a drummer (e.g.The Beatles, KISS, Foo Fighters, Weezer, Metallica, The Clash, Creedence Clearwater Revival, The Kinks, The Fray, Sonic Youth, The Smashing Pumpkins, and the new lineup of Wolfmother). This is popular with bands for its versatility. However, it has been noted the main complaint is that it takes too much effort to keep so many instruments in tune when they are played by every member of the band.
Another common formation was a vocalist, electric guitarist, bass guitarist, and a drummer (e.g.The Who, Led Zeppelin, The Ramones, Sex Pistols, Red Hot Chili Peppers, Queen, R.E.M., Blur, The Smiths, Echo and the Bunnymen, Stone Roses, Creed, Black Sabbath, Van Halen, The Stooges, Joy Division, U2 and Coldplay). Instrumentally, these bands can be considered as trios. This format is popular with new bands, as there are only two instruments that need tuning, the line-and-counterpoint formula prevalent with their material is easy to learn, four members are commonplace to work with, the roles are clearly defined and generally are: melody line, rhythm section with counterpoint melody, and vocals on top.
In some early rock bands, keyboardists were used, performing on piano (e.g., The Rolling Stones initially used Ian Stewart on piano), The Seeds and The Doors with a guitarist, singer, drummer and keyboardist. Some bands will have a guitarist, bassist, drummer, and keyboard player (for example, Small Faces, King Crimson, The Guess Who, Pink Floyd, Coldplay (during some of their later work) and Blind Faith).
Some bands will have the bassist on lead vocals, such as Thin Lizzy, Chameleons, Pink Floyd, NOFX, +44, Slayer, The All-American Rejects or even the lead guitarist, such as Dire Straits and Creedence Clearwater Revival. Some bands, such as The Beatles, have a lead guitarist, a rhythm guitarist and a bassist that all sing lead and backing vocals, and also play keyboards regularly, as well as a drummer.
A string quartet usually consists of two violins, a viola and a cello. An upper string quartet features two violins and two violas. A lower string quartet features 1 viola, 2 cellos and a double bass. An American string quartet features two guitars, a banjo and a ukelele.