Set of 2 - Acoustic Foam Studio Half Moon Corner Block Wall Finish Acoustic 18" X 9" X 4.5" Color: CHARCOAL; Best used with Acoustic Bass Traps, TriAmps, Wedges, Pyramids, Eggcrates 18" X 9" X 4.5" ; Noise Reduction: 80-90% Eliminates Standing Waves And Flutter Echoes; Reduces Unwanted Reflections; Reduces Unwanted Reflections Good for studios, recording studios, vocal booths, control rooms. Product Care: Occasional Vacuuming of Dust