Originally Posted by Or
Thank you for your comments. I will consider it and probably replace both front and rear speakers. There is no plug-in replacement for the door-mirror mounted tweeters, so I'll ignore them.
A 5.25" speaker is the best that will fit in the door w/o a lot of cutting and altering, and custom grilles. I'll stick with that size though I understand your point. Coming home on Tuesday, I did some experimenting. Now knowing the front doors were only mid-woofers, I played with more rear fade and the sound clarity jumped dramatically. Also, I popped one of the rear grilles just to look at the rear pillar 4" speakers. When I did so, an "extra" paper tweeter cone fell out of the left one. Apparently, it had been in there since new and was a manufacturing error. That helped sound quality a lot, too!
Component tweeters almost always require some handiwork to fit into stock locations.
If Crutchfield says some 6.5" speakers will work, I'm inclined to believe them, and urge you to try. They wouldn't make such recommendations if it required a lot of work, esp. considering their target market can be considered largely neophytes. And if they don't fit, then they'll either help you, or take them back, which is what their higher pricing helps support.
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By "sealed against the mounting plane" do you mean have an acoustic baffle behind, like stretching some PE sheeting to cut down on feed back bouncing off the outer door? Or more of a baffle? Effectively making an enclosure? I'll do as you suggest but am unsure what this is (I'll google it to educate myself).
When you mount the drivers, you want to make sure there aren't any gaps around the perimeter between the speaker frame and the surface it's mounted to, allowing air to pass. Some manufacturers even include a little bit of sealing tape with their products. If not, some weatherstripping can be used instead.
Those foam cup baffles, both stock and aftermarket, also provide that function, but they're mostly to protect the speaker from the elements. But by sharply reducing the volume of space behind that speaker, they can actually hurt sound quality by not allowing the fuller volume of the door cavity to be used. Some people either cut openings in them or remove them altogether.