They are 4 ohm auto versions. I have heard they are very sensitive. I did hear them in a demo car years ago and loved them. My understanding was use very clean amplification, high xovors points, and everyone says have a cap in line for protection. I see old threads regarding caps, I just dont know if the caps change per driver discussed or can I just any cap on this tweeter. Also, what is the best way to wire them in?