So i have a friend that shows me Prefab bandpass boxes and i keep telling him not to waist his money and build it himself or find someone who knows what they are doing (he only has 2 p2s i think at the moment). I don't know much about Rockford subs or what the box specs are let alone for 4 of them. He also doesn't get what i mean by prefabs being cheap and not having the right tune. He think i mean tuning his head unit or amp. So basically what is the proper tune for a ported box for four P3D4-12s so i can tell him to find someone and just tell them you want a ported box tuned to -blank- for four p3's to fit what ever his trunk size is. I know it sounds kind of stupid to tell someone to do that without explaining more. He also lives in Arizona so if anyone knows a trusted builder around that area that would help as well.

What vehicle?

I would suggest no less then 4 cu.ft @35hz depending on the owner of the subs is wanting.....If it was me I would do 5 cu.ft @32hz... Unless if he would want it to sound like total garbage and last for a few weeks..For fun I would do 8 cu.ft @38hz..lol