Here are some picture of how I put some MB QUART RKC 113 5.25" in the rear doors of an extended cab. Had to cut out the speaker holes a little bit. Then made some spacers. .700 long for the top and .300 long for the bottom so the speaker would clear the back side of the door skin. The crossover fit under the pull handle.
It made a big difference. I don't know why I didn't do this a long time ago.

 

Dude, that's sweet...I'm sure that is gonna catch on around here with the stereo guys.

 

i just ended up putting 4x6 there and skipped hte cutting part.

you think 6.5 would fit if you cut more?

 

Why bother? Create an overwhelming front soundstage, and you wont need rear speakers.

Having mid-bass come from the rear will ruin the imaging of the entire stereo.

 

I don't think so. I never though it would make such a difference because they are just filler speakers, but know that I have replaced them I don't think that anymore. It made a big difference. The sound is night and day difference sitting in back. From the front the cab sound way more even and full.

 

I didn't go with 6 1/2 because I didn't want to cut the door panel. I like the door speakers to be behind the door panel for a clean look. The opening and the grill in the door panel is a little small than 5 1/4, so to put a 6 1/2 in it would be covering up the extra 5/8 per side that you gain in speaker size.

I don't remember the speaker depth, but whatever it is I have about an 1/8 of an inch between the door skin and the speaker. So if you can find some good shallow 6 1/2 they would fit.

 

That is awesome man, when I getting around to doing my sound system that is the route I'm gonna take.

 

I put a set of 4" components with a seperate tweeter. I tell you it made a bid difference in sound back there.