well i had just one of these 12s in a prefab box that for some reason had 2 ports with different tunning. it had 1 earo port that was suppose to be at 38hz and then its had a second chamer inside the box that looked kinda like a L shape slot port but then that chamber was ported with a earo port at 42 hz. that peaked at 48hz. then i had a box with to small of port erea tuned to 41 hz that peaked at 45hz ( 1 12 here to ). the box was built using the box design in the manual for the sub. but the guy that i know at the shop i go to knows a lot about rockford and talked to the rockford tech and they agreed with a slot port like my design it would be loudest at or near 43-45hz.
hn155: Rockford punch pro speakers, t400.4 deh 80prs, full audio build to come. working towards 175hp n/a, simple but fun.