I have the sub box for 2 12" subs its a typical box that you would find in a camaro or firebird I was thinking if it would be a good idea to make it out of carbon fiber. Would it hold up and not crack? Would it sound good? The reason for carbon fiber is for light weight because the wood box is heavy

 

Outside of making it insanely expensive, I would think that a carbon fiber box would have a lot of flex in it. Flex means wasted energy and nasty reflective waves inside and outside the enclosure. If you're worried about weight, pull the box before you race.

 

Weight is always an issue the less the weight the faster yes you can take out the box and race but I want to be able to have my music with out removing it I was thinking carbon fiber for light weight but that is already not looking good what other alternatives is there on sub box that are a bit lighter with out messing with the way it will sound

 

many have made boxes out of fiberglass (quite a few layers) with good results. you can further brace it by putting in rope/twine to give it a frame of sorts, just put it about half way through the layer process

 

So a fiberglass box would be lighter than the standard wood box for our thirdgens

 

correct. for ease of install/building, i would do a hybrid of sorts; mdf top (carpeted to match the rest of the hatch area of course) and fiberglass sides/bottom. another benefit is that its waterproof in case you spring a leak in the weatherstripping

 

What I would do is first make the bottum portion of the the box out of fiberglass.
Then cuts some rings that you speakers will mount to out of mdf, and 4 pieces of
cut in strippes to go from the bottum of the box to the mounting rings for the
speakers, attach with screws. then fiberglass or use carbonfiber to make the top.

 

I tried one outta fiber glass.. but it flexed too much and damged the subs. < the suspension/voice coils

 

this is great info going to tell my homie to build me one