can you run a speaker with a tweeter, mid range, and mid bass off of the HU or do you need a cross over or a high pass from an amp because of the tweeters. or does it already have a crossover built in to keep the tweeter from recieving bass?
If you're talking about normal as in the ones you buy as a package, yes, they come with crossover built in. You can run it off your HU but the sound quality will be limited. For better result, you'll need a separate amp.
3-way speaker systems (tweeter, midrange, midbass) have their own 3-way crossover modules for the speakers. You will need an amplifier for any 3-way system though. They need plenty of power to move the midbass driver and give good response for mids and tweeters. Running off of a head unit will sound very muffled and barely audible for volume.