An exemplary retainer ring for a head of an acoustic drum can produce a visual display that allows an observer to visualize timing associated with percussive sound. An exemplary retainer ring includes a vertical wall disposed at a radius about a central axis and a laser diode module that includes a lens to emit visible radiation as a fan-beam. In such an exemplary retainer ring, the lens is positioned such that the fan-beam crosses the central axis and terminates as an arc in a groove in the vertical wall. When an object interrupts the fan-beam, the object reflects visible radiation of the fan-beam to thereby produce a visual display that allows an observer to visualize timing associated with percussive sound (e.g., sound produced by the object contacting a head of an acoustic drum). Various other exemplary arrangements, devices, systems, methods, etc., are also disclosed.