Tedd A Jander:

>I know that antiphonal means alternating singing or playing by separate
>groups of performers, but exactly how does the word "antiphonal" pertain
>to the sacred choral music of the Renaissance and its affect acoustically.

The different choirs would be separated physically, perhaps at a
considerable distance, so the listener would hear the music coming from
different directions.  The size of the groups might be quite different
also.

Jim Tobin