Just upgraded the door speakers with JBL 6x9's -. $83 GX963 300W 6" X 9" 3-Way GX Series Coaxial Car Loudspeakers (Pair of 2, 600W Total),black. GX963. After installing those, I used a pink noise generator and adjusted the treble, mids, and bass to an almost flat frequency response. More @Wikipedia
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