... perforated metalMaterialCarbon steel, Aluminum, Brass, Copper.FinishPowder coated,galvanized,polished,or no finishHole shapeRound, Square, Slot, ... Long hole, square hole, round hole, hexagonal hole, scale hole, stretching and other special-shaped hole.· Hole style: ... barriers, architectural objects, walls, generator room, factory premises, and other noise acoustic noise sources using sound-absorbing ...