Choir is an ensemble.
Choir . Choirs may sing without instrumental accompaniment , with the accompaniment of a piano or pipe organ , with a small ensemble ( e.g. , harpsichord , cello and double bass for a Baroque era piece ) , or with a full orchestra of 70 to 100 musicians . The term `` Choir '' has the secondary definition of a subset of an ensemble ; thus one speaks of the `` woodwind choir '' of an orchestra , or different `` choirs '' of voices or instruments in a polychoral composition .