I suppose since the E46's have been out a while now, people are getting them used and starting to do their audio upgrades to them. I will share what I learned from self-installing my system in a 2003 325i.
The setup is -
Left and Right 1.5" Tweeters in the doorframe, on the inside of the car pretty much next to your mirrors.
Left and Right 3.5" Mid-Range centered in the middle of the doorpanel
Left and Right .. now this gets weird. They are 120mm speakers which is roughly 6.7", and they are 3 screw'd with weird angles, so your option is to custom fit the panel or do what I did. Buy 5.25" speakers and you can just clip out the plastic ring that held the orriginal speaker in and secure it that way, it fits the whole speaker perfectly in the ring that was to hold the stock speakers in.
Left and Right 1.5" rear tweeters right behind each front seat.
Left and Right 6.7" rear deck speakers, I didn't change these, so im not sure how to swap for aftermarket.
The stock speakers (non-HK) can easily handle the power I was putting to them with my JL 500/5 amp. They're high quality.
The front tweeter and the mid-range are on a crossover ..
There is a wiring guide for the factory head unit and amp that I posted in this area a while back, i'll edit when i find the post again, you can search for now.
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