Dynamat extreme door kit.
Even the best new speakers cause speaker panel distortion. Home audio speakers typically come in well crafted, heavy boxes to eliminate this distortion--a solution that is impossible (or at least impractical) in your car. For your car, Dynamat is the solution.
Applying Dynamat to the car door surrounding your speakers eliminates speaker panel distortion by transforming the flimsy sheet metal into a solid non-resonant baffle.
Dynamat improves mid-bass performance and stops vibration rattles and squeaks. Your stereo will sound its very best with Dynamat.