I'm looking to get some subwoofers from crutchfield.com. I want to make my own sub box and are wondering if these dimensions would be sufficient. The subs are 12" and they are sony XS-L1200B, they have a bottom mount depth of 4 15/16 and a top mount depth of 5 9/16? What are those? Well I want to make my sub box 14" high, 28" long and probably about 7" width. Also I'm wondering if this will be a hard task with my grand am 97 four door. Also, will I need a cap for 400 watts?

Depending on the dimmensions of your trunk and how high you can make a box. I would say if your putting 12"s in, make the box atleast 16" high, leaving 2 inches around the speaker. for 400 watts i doubt youd need a cap.

you cant just make a box you need to find out what the speakers need for air space then build form there like 1 sub needs 1.2cubic ft there for the inside diamater needs to be 1.2 get it cool