Originally Posted by somebody else
How much are the tweeter upgrades?
I replaced all 4 door speakers on a standard Premium Hatch (no add-ons) with Polk db 651s (the "s" is for slim or shallow depth) and get wonderfully balanced sound throughout the range. I didn't and still don't know if regular Polk 651 will fit but there is plenty of space to shim them out if they don't. I wish I had got these as they add an additional 15 Hz to the bottom end -- from 50 Hz to 35 Hz. Paid $120 for all four. These are well-built units and weigh over 3x what the stock speakers weigh. They are still breaking in and sound better every day. More than enough high frequency despite the low mounting position.
You do know that the primary reason to add the tweeter kit is to change the location to where it echos off the windshield right at ear level, right?
Did you disable the dashboard tweeters? Do you know how the signal is split for the door woofer and dash tweeter? Does all the signal go through the woofer first then go to the tweeter with a high pass filter or is there a passive crossover before the signal even reaches the speakers that splits the signal to the woofer and tweeter independently?