The Gardner Museum’s Calderwood Hall is the kind of space that can quicken the pulse with its novel visual design. But by seating the audience on all four sides of the performers, the space poses unique challenges for singers in particular. To whom, exactly, should you sing?

At her recital on Sunday afternoon, the mezzo-soprano Isabel Leonard adopted the sensible compromise of a slow spin, directing individual songs to different sides of the hall, and even went as far as apologizing for turning her back on those audience members seated behind her at any given moment — in effect, half of the hall.