What a great install for a stupid device.

A proper install + a proper headunit would fix all of that. And if you didn't want the head unit, amps have gain control and all you should have is a pot for volume, not a full blown frequency shaper. Ah well.

http://rs.audiocontrol.com/company_3..._SalesNote.pdf

Cars peaking at 120 Hz? Since when? They typically peak around 30 Hz or lower. Having a water tight cabin means air pressure has some difficulty getting out.