A head stack assembly for a disk drive includes a rotary actuator assembly. The rotary actuator assembly includes an actuator body having a bore defining a pivot axis, an actuator arm cantilevered from the actuator body, and a coil portion cantilevered from the actuator body in a direction opposite from the actuator arm. The coil portion includes a coil support, a flat coil supported by the coil support, the flat coil including a coil surface generally perpendicular to the pivot axis, and a constrained layer damper attached to the coil surface. The constrained layer damper includes a stiffening layer having a coil-facing planar surface generally perpendicular to the pivot axis and an adhesive layer positioned between the coil-facing planar surface and the coil surface.