The Atrium 45 speakers are designed to be rustproof with all stainless steel and aluminum hardware that meets all corrosion and salt tests. They feature a sculpted front baffle and rounded enclosure which minimizes sound diffraction as well as rustproof aluminum grilles that have 55% open area for improved sound quality. The speakers come with rustproof aluminum brackets which rotate 90 degrees for sound optimization and allow for multiple mounting positions. They are available in a black finish or in a white finish that can be painted to match your decor and come with a 2 year warranty. The main differences between the Atrium 45 and Polk Audio's Atrium 45p is that the Atrium 45p is meant only for indoor use, is self-powered, and has built-in controls, while the Atrium 45 requires an amplifier and can be used both indoor and outdoor.