I installed a set of speakers in the rear pillar, where I previously had none. Any 3 1/2 inch speaker will work in the recess. All you really need is some self-tapping sheet metal screws (small ones) and screw them right in. It took me about 10 minutes per speaker and I just tapped into the pre-existing wiring. I bought a pair of Infinity 3.5 two-ways. They won't blow you doors off, but the get the job done. Anything any bigger won't fit.
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