Choirs are often led by a
conductor or choirmaster. Most often choirs consist of four sections intended to sing in four part harmony, but there is no limit to the number of possible parts as long as there is a singer available to sing the part:
Thomas Tallis wrote a 40-part
Spem in alium, for eight choirs of five parts each;
Krzysztof Penderecki's Stabat Mater is for three choirs of 16 voices each, a total of 48 parts. Other than four, the most common number of parts are three, five, six, and eight.
Choirs can sing with or without instrumental accompaniment. Singing without accompaniment is called
a cappella singing (although the
American Choral Directors Association
 discourages this usage in favor of "unaccompanied," since a cappella denotes singing "as in the chapel" and much unaccompanied music today is
secular). Accompanying instruments vary widely, from only one instrument (a piano or pipe organ) to a full
orchestra of 70 to 100 musicians; for rehearsals a
organ accompaniment is often used, even if a different instrumentation is planned for performance, or if the choir is rehearsing unaccompanied music.
Many choirs perform in one or many locations such as a church, opera house, or school hall. In some cases choirs join up to become one "mass" choir that performs for a special concert. In this case they provide a series of songs or musical works to celebrate and provide entertainment to others.
Role of conductor
Conducting is the art of directing a
musical performance, such as a choral
concert, by way of visible gestures with the hands, arms, face and head. The primary duties of the conductor or choirmaster are to unify
performers, set the
tempo, execute clear preparations and beats (
meter), and to listen critically and shape the sound of the ensemble.
The conductor or choral director typically stands on a raised platform and he or she may or may not use a
baton (using a baton creates more visible gestures. Many choral conductors use their hands to conduct. In the 2010s, most conductors do not play an instrument when conducting, although in earlier periods of
classical music history, leading an ensemble while playing an instrument was common. In
Baroque music from the 1600s to the 1750s, conductors performing in the 2010s may lead an ensemble while playing a
harpsichord or the violin (see
Concertmaster). Conducting while playing a
piano may also be done with
pit orchestras. Communication is typically non-verbal during a performance (this is strictly the case in
art music, but in jazz
big bands or large pop ensembles, there may be occasional spoken instructions). However, in
rehearsals, frequent interruptions allow the conductor to give verbal directions as to how the music should be sung.
Conductors act as guides to the choirs they conduct. They choose the works to be performed and study their
scores, to which they may make certain adjustments (e.g., regarding tempo, repetitions of sections, assignment of vocal solos and so on), work out their interpretation, and relay their vision to the singers. Choral conductors may also have to conduct instrumental ensembles such as
orchestras if the choir is singing a piece for choir and orchestra. They may also attend to organizational matters, such as scheduling rehearsals,
 planning a concert season, hearing
auditions, and promoting their ensemble in the media.