the port may be welded inside the box. like maybe they did it through the speaker holes. also to whoever said it 1/4 inch aluminum is flimsy compared to 3/4 mdf. once you get any kind of long span in it the metal would flex all over the place. 3/8 aluminum is a different story though.much more heavy duty even though its only 1/8 inch thicker. I work for a pontoon boat company so I see tons of aluminum.