The back room at Barbès, a dark little hole-in-the-wall on Ninth Street in Park Slope, is separated from the front bar by a thin wall with a window cut out of it, the way a garage might be separated from a basement rec room. Depending on what night you stop by, the music coming from back there can be almost anything—“mangue beat” music from Brazil one night, a Hank Williams honky-tonk cover band the next night, and on the weekend, a guy who “explores and re-creates the music of the great French accordionists of the thirties.” You learn to be surprised.