Greetings to you! I am not quite satisfied with the sound of my system (performance loudspeaker, HU-650). in things home-hifi I know myself very well, but in the car I am rather still green behind the ears. after many researches here and in other foren showed as the first step the insulation of the doors and the retrofitting of an amplifier. but now I have received two of my considered good offers from a dealer: – four used high performance deep-tones around 160€ – four used premium deep-tones including pa-300 by 500€ when I already take apart the doors and dam, then I build the higher-quality ls one! can only become better. now my questions: – with “high performance” and “premium” are then only additional tweeters installed in the front doors, or? in the back doors there are no ones and those remain in the D-pillar (with both of the standard systems are too) or the “high-high-ranges”?