Polk DB522 5.25" Coaxial Speakers with Marine Certification Perfect for anything: Cars, Trucks, Boats ATVs & More. Everything you love about Polk’s Dynamic Balance technology—that rich, clean, full-range sound—is built into the marine-tough, yet ruggedly sophisticated, DB+ series. And with its universal fit, it can be installed in any vehicle: Automobiles, motorcycles, boats, ATVs—you name it.