Echo

One source on the left, lit and breathing. Every six seconds it fires a single ring outward. The ring expands until it meets a wall, then a return ring is born from the wall’s mirror of the source — top first, bottom next, then the right edge, finally the left wall behind the source itself. Each return is dimmer than the last; each return can return again. Pulses overlap. The canvas is usually carrying three or four generations of rings at once, some outbound, some homebound. The signal travels; what comes back is the room.