Summary: I bought a set of the 5s last summer for a custom install in my Ultra Classic lowers. Sad thing is that they sound better and louder than my 4" Boston Acoustics in my dash. Marine grade is the way to go every time!!! Buy them you'll love them!! Just make sure you are running an amp to them they love the watts!! Soundstream is the amp I'm using in my tour pack.
Summary: Mounted these in the rear position in my corolla wagon... It's amazing how efficient these polks are, and even the little 4" ones sound great...nothing but a Pioneer head unit hooked to them, but nearly too loud for my aging ears! I'll add a 50 watt x 4 channel amp in the future to clean up the LOWEST bass, but plenty happy for now! The marine rating is perfect for where I live,,,,in the rain forest of northwestern Oregon!
Conclusion: I have 2 of these in the front. They are very good at picking up high sounds and very clear. Not good if you want to crank it up with bass though obviously since its a 4 incher. Not bad for 4 inchers certainly.
Conclusion: I bought these to mount as a center channel setup in my 1986 Chevrolet Crew Cab's original 4x10 dash slot. It took some modifications and building a custom plate for them, but they fit better and sound better than a single 4x10, which I tried before ordering these. They work great and I achieved what I was looking for.
Conclusion: I have owned many sizes of speakers of this same type of speaker. from Polk. From 3-1/2 to the 6x9s. All of them sound great but all of them were running off of the head unit. A lot of people have said to really appreciate these speakers they need to be hooked up to an amp. In this case they are hooked up to a 4 channel JL Audio amp. I have 110 watts per channel going to 4 of these speakers in a custom molded headliner.
Conclusion: Very efficient; very very loud, smooth and clear in the vocals range. Treble is not ovepowering but is decent. I can't rate the bass because I have a sub and whatever bass may be coming out is totally washed out obviously. Bass coming through the speaker does not distort the mids/highs which is a good surprise.