Open structure and exposed ductwork are often 12–20 ft. Open ceilings add a large volume of air above the room, so reverberation times are long.
At 500 Hz the bare ceiling absorbs about 5% of the sound that reaches it. In a room with a hard floor, the ceiling and floor reflect sound back and forth, so treating the ceiling is often the single most effective step.
Options: clouds, baffles or ceiling tiles.