This year marks the 15th of existence for Georgia quartet Perpetual Groove. The group has become a titan of the jam-band scene. While it gathered a following in its early days around the college towns of Savannah and then Athens, Georgia, the group quickly became a favorite of fans of live improvisation when it started wider U.S. tours in 2003. Where many jam acts have, of late, incorporated bluegrass, folk, and brash flourishes, Perpetual Groove has always been one of the more staunchly rockcentric acts in its circles. With just a touch of synth loops and maybe a little jazz, the group's circling explorations often sound like a slightly stripped-down version of prog. With the average song reaching almost ten minutes, though — and that's in the recorded version! — there is definitely enough material to last over the group's two-night stand at Culture Room.