Madrigal singers

A madrigal is a secular vocal music composition, usually a partsong, of the Renaissance and early Baroque eras. Traditionally, polyphonic madrigals are unaccompanied; the number of voices varies from two to eight, and most frequently from three to six. It is quite distinct from the Italian Trecento madrigal of the late 13th and 14th centuries, with which it shares only the name.

Madrigals originated in Italy during the 1520s. Unlike many strophic forms of the time, most madrigals were through-composed. In the madrigal, the composer attempted to express the emotion contained in each line, and sometimes individual words, of a celebrated poem.

http://en.wikipedia.org/wiki/Madrigal