The Sirens, an all-female ensemble, aren’t quite as sharp as usual in their new long-form improv show. Beginning with a sketch created from references in a pop song, the six cast members create a series of scenes with recurring characters. The performers were at a disadvantage the night I attended because the audience was extremely small. Perhaps that’s why they relied on inside jokes that made the ensemble members offstage chuckle while the audience looked on puzzled. Several sketches seemed murky and directionless, and the show never felt cohesive. Yet the Sirens’ energy remained high, they got some laughs and maintained a sense of spontaneity, and they managed a strong ending. Maybe the show will get better as it goes along. Through 12/16: Thu 8 PM. Strawdog Theatre Company, 3829 N. Broadway, 773-509-6433. $8-$12.