Suspended T-bar grid ceilings are usually 8–10 ft. Standard mineral fiber tiles absorb well (NRC 0.50–0.70), but cheap vinyl-faced or damaged tiles may not.
At 500 Hz the bare ceiling absorbs about 55% 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.