The Assembly of the Sacred Wheel’s chant albums were created with the intention that the chants be simple, powerful, and easily performed by individuals and ritual groups. They are mostly a cappella with some percussion and an occasional instrument to ease there use in covens, circles, groves, etc. Most of the chants do not require a wide singing range and the harmonies, while pretty, are not necessary.
Source: Chant Albums From The Assembly of the Sacred Wheel