Vaulted and cathedral ceilings are sloping from 8 to 20 ft or more. Sloped ceilings focus reflections towards one end of the room and add volume.
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.