I dont know how they are set up on 3rd or 5th gens, but on 4th gens it looks like there is an ideal spot to place tweeters in that little plastic grill type piece right at the bottom of the windshield. On either side onf the vent there looks to be just enough room, and on professional audio systems, I have seen many tweeters placed here.

Has anyone done this or seen this?

Just an idea.
James

 

You can put the tweeter in the same place as the 5th gen Maximas but it is not the most ideal place. The best place is in the door not more than 7-8 inches away from your mids for the best imaging. If you place the tweeter more farther away from the mid you lose alot of imaging.