Olif

First off, I'm sorry if I'm asking a dumb question or one that been asked before, I'm new this. So I want to build a system in my 93 explorer and wanting to install 6.5'' midrange speakers in all 4 doors with tweeters in the front, but was wondering if I can run them separately or if I need a crossover, and if I do need a crossover how much more power per channel will I have to run? Thanks