how much depth is needed to clear the window glass?
I have an old pair of Alpine 6663's (top-of-line coax from it's day), but I don't know how much rear clearance I'll need, nor how much front clearance I have before it hits the door panel.

 

i dont know but i ordered my 6.5 kickers so maybe next week i can find out how deep we have to play with. ill most likely go to a stereo shop and see if i can but the ring spacers my self.

 

I never found 6.5" trim rings so I made mine. Take your 6.6 and lay it face down. Trace around it and then measure 1/2" inside that ring and draw another. Then cut it out and sand the edges smooth. I have a router but this was easier for my with a jigsaw.

 

damn i have no wood cutting tools at all! man i hope i can find some at my local stereo store

 

So how thick should the spacer be?

 

standard sheet of MDF is 5/8 or 3/4 depending on where you buy it. You obviously dont need a full sheet though at $30 a sheet. See if a shop has some scrap or Lowes/Home deoot has some partial sheets or something damaged