Sound, space and movement all share an equal role in Urban ECHO, where Leah Stein Dance Co. and the Mendelssohn Club of Philadelphia play the Rotunda. And they play it several ways: by creating sounds; physically (tapping fingers on the floor), or using the structure\'s echo-producing acoustics to aurally envelope the audience; along with exploring architectural elements here. Most surprising is the role of the large choral group, who are as much a part of the action as they are of the sonics. The wordless score, by Pauline Oliveros, emphasizes timbre and tonality; meanwhile the cumulative impression is of a broad conceptual experiment that highlights the communal effect of live performance.