Just because people tend to sit down while watching Off Broadway's roots- and folk-heavy acts, don't think this south-city club doesn't know how to rock. No matter how understated acts like the Long Winters and Bobby Bare Jr. might sound on record, you can bet that when they show up for work at this multilevel joint they'll be turning the volume knob clockwise. More than twenty years young, Off Broadway appeals mostly to the socially liberal and fiscally conservative (those who like cheap drinks, anyway). But everyone always seems to get along. Perhaps the sitting down has something to do with it.