In music, a quartet or quartette (French: quatuor, German: Quartett, Italian: quartetto, Spanish: cuarteto, Polish: kwartet) is an ensemble of four singers or instrumental performers; or a musical composition for four voices or instruments.
String quartet 
In Classical music, the most important combination of four instruments in chamber music is the string quartet. String quartets most often consist of two violins, a viola, and a cello. The particular choice and number of instruments derives from the registers of the human voice: soprano, alto, tenor and bass. In the string quartet, two violins play the soprano and alto vocal registers, the viola plays the tenor register and the cello plays the bass register.
Composers of notable string quartets include Joseph Haydn (68 compositions), Wolfgang Amadeus Mozart (23), Ludwig van Beethoven (17), Felix Mendelssohn (6), Franz Shubert (15), Johannes Brahms (3), Antonín Dvořák (14), Alexander Borodin (13), Béla Bartók (6), and Dmitri Shostakovich (15). The Italian composer Luigi Boccherini (1743–1805), wrote more than 100 string quartets.
Less often, string quartets are written for other combinations of the standard string ensemble. These include quartets for one violin, two violas, and one cello, notably by Carl Stamitz (6 compositions) and others; and for one violin, one viola, and two cellos, by Johann Georg Albrechtsberger and others.
Piano quartet 
Another common standard classical quartet is the piano quartet, consisting of violin, viola, cello, and piano. Romantic composers Beethoven, Brahms, and Mendelssohn each wrote three important compositions in this form, and Mozart, Dvořák, and Gabriel Fauré each wrote two.
Other instrumental quartets 
Wind quartets are scored either the same as a string quartet with the wind instrument replacing the first violin (i.e. scored for wind, violin, viola and cello) or are groups of four wind instruments. Among the latter, the SATB format woodwind quartet of flute, oboe, clarinet, and bassoon is relatively common.
An example of a wind quartet featuring four of the same types of wind instruments is the "Saxophone Quartet", consisting of Soprano Saxophone, Alto Saxophone, Tenor Saxophone and Baritone Saxophone or (SATB). Often a second alto may be substituted for the Soprano part (AATB) or a Bass Saxophone may be substituted for the Bari. The groups usually perform a mix of classical and jazz. Saxophone Quartet literature is limited and most of the traditional style classical sheet music is transcribed from string quartet charts.
Vocal quartet 
Compositions for four singers have been written for quartets a capella; accompanied by instruments, such as a piano; and accompanied by larger vocal forces, such as a choir. Brahms and Schubert wrote numerous pieces for four voices that were once popular in private salons, although they are seldom performed today. Vocal quartets also feature within larger classical compositions, such as opera, choral works, and symphonic compositions. The final movement of Beethoven's Ninth Symphony and the Verdi Requiem are two examples of renowned concert works that include vocal quartets.
Typically, a vocal quartet is composed of:
- Soprano, Mezzo-Soprano, Tenor, and Baritone or Bass, for mixed ensembles; or
- 1st Tenor, 2nd Tenor, Baritone, and Bass, for male groups; or
- 1st Soprano, 2nd Soprano, Mezzo-Soprano, and Contralto, for female groups.
Quartets are popular in jazz and jazz fusion music. Jazz quartet ensembles are often composed of a "horn" (e.g., saxophone, trumpet, etc.), a chordal instrument (e.g., electric guitar, piano, Hammond organ, etc.), a bass instrument (e.g., double bass or bass guitar) and a drum kit. This configuration is sometimes modified by using a second "horn" replacing the chordal instrument, such as a trumpet and saxophone with string bass and drum kit, popularized by Miles Davis, or by using two chordal instruments (e.g., piano and electric guitar).
Popular music 
Some well-known female US vocal quartets include The Carter Sisters; The Forester Sisters; The Chiffons; The Chordettes; The Lennon Sisters; and En Vogue. Some well-known male US vocal quartets include The Statler Brothers; The Ames Brothers; The Chi-Lites; Crosby Stills Nash & Young; The Dixie Hummingbirds; The Four Aces; Four Freshmen; The Four Seasons; The Four Tops; The Cathedral Quartet; Ernie Haase and Signature Sound; The Golden Gate Quartet; The Hilltoppers; The Jordanaires; Mills Brothers; The Rascals; and The Skylarks. The only known U.S. drag quartet is The Kinsey Sicks. Some mixed-gender vocal quartets include The Pied Pipers; The Mamas & the Papas; The Merry Macs; and The Weavers.
The quartet lineup also is very common in pop and rock music. A standard quartet formation in pop and rock music is an ensemble consisting of two electric guitars, a bass guitar, and a drum kit. This configuration is sometimes modified by using a keyboard instrument (e.g., organ, piano, synthesizer) or a soloing instrument (e.g., saxophone) in place of the second electric guitar.
See also 
- Allen, Ray. Singing in the Spirit: African-American Sacred Quartets in New York City, in series, Publication[s] of the American Folklore Society: New Series. Philadelphia, Penn.: University of Pennsylvania Press, 1991. xx,, 268 p., ill. with b&w photos. ISBN 0-8122-1331-9 pbk.
- Random House Dictionary. "Quartet". Dictionary.com. Retrieved 12 January 2013.
- Merriam-Webster. "Quartet". Merriam-Webster, Inc., div. of Encyclopaedia Britannica. Retrieved 12 January 2013.
- Apel, Willi (1975). "Quartet". Harvard Dictionary of Music. Second: 711. ISBN 0-674-37501-7.
- dailymail (9 June 2011). "Million Dollar Quartet: A toe-tapping night of music perfect for Father's Day". Daily Mail (London).