Cori spezzati (kor' ee spetz ah' tee), Italian for "separated choirs," is the term used to describe a musical composition that uses spatial effects to emphasize the interplay between its various voices. Typically, this means placing two or more choirs or groups of instruments in various places around a performance space. Music that is intended to be performed cori spezatti is by nature antiphonal; in fact, some consider these two terms to be synonymous, at least when they refer to instrumental music.
Cori spezzati isn't a particularly common form of music, and for obvious reasons. In order for it to work out right, it must be performed in a specific type of space; namely, one which is both big enough to accomodate the separation of the instrumental/vocal groups and acoustically suited to the kind of call and answer phrasing that characterizes antiphonal music. (If the space is too echoey, the interplay among the groups just becomes muddled. If it's just moderately echoey, though, it sounds great.) And even in concert halls which meet these specifications, there's a certain awkwardness to the idea of putting half the ensemble onstage and sending the rest up to the balcony or (as I have seen done) forsaking the stage altogether and having half the group stand in the left-hand balcony and the other half in the right-hand one.
The type of performance space which is most obviously suited to cori spezzati is the cathedral; in churches, the problem of the stage is eliminated, and there are generally balconies and nooks and crannies galore in Renaissance-style basilicas. Unsurprisingly, a Renaissance basilica was the formal birthplace of cori spezzati: in the late 1500's, Giovanni Gabrieli, the music director, organist, and composer-in-residence at St. Mark's Basilica in Venice, began experimenting with the idea of separating his choirs and putting them in different places around the church. Gabrieli is considered to be the father of cori spezzati, and probably the only composer to write a serious volume of work in this style. He wrote both choral and instrumental pieces (mostly sacred, because of the nature of his job), some of which are still performed today and shouldn't be too hard to find recordings of. (I, unfortunately, do not own recordings of any of Gabrieli's music, although I heard his Sonata Octavi Toni for two brass choirs performed live, and it was gorgeous. I recommend it highly if you happen to like Renaissance/Baroque music.)
This writeup was made possible by a little bit of help from www.naxos.com/composer/gabrieli.htm, and Virginia Tech's Online Music Dictionary, found at www.music.vt.edu/musicdictionary
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