Auralex GeoFusor 11 Diffusor, 4-Pack

Absorption removes acoustic energy from a room; diffusion scatters it instead, which is what the GeoFusor is built for. Its geodesic dome shape breaks up reflections into a uniform, highly dispersive pattern that counters standing waves and flutter echo while keeping the room's liveliness, useful anywhere from a critical listening space to a live room tracking drums, brass, or woodwinds.

This is the 1 ft x 1 ft GeoFusor 11 sold as a four-pack, small enough to mount on a wall or ceiling in a cluster rather than committing a whole surface to one large panel.