Keyboard percussion instruments such as xylophones and glockenspiels are composed of an arrangement of bars. These are varied in some of their geometrical properties-typically the length-in order to influence their acoustic behavior. Most instruments in this family do not deviate from simple geometrical shapes, since designing the natural frequency spectrum of complex shapes usually involves a pain-staking trial-and-error process and has been reserved to gifted artisans or professional manufacturers. In our work, we propose an automatic approach for creating novel instrument designs in a general setting far beyond 2d plates. Our goal is to develop a framework that takes a target shape, a target pitch, and material properties as inputs. With the help of an optimization routine, a 3d solid is then synthesized that matches both the target shape and pitch as closely as possible when fabricated out of the specified material.