I have a 03 cavalier with a g34 yellow top and a single 3512 running at .7ohms on a very old school us amps 100hc running maybe a little over 1k watts. i built 2 boxes so far for this one 12" (was testing with a 12" bass mekanik before) one for street bass so it wasn't that loud on the TL. The SPL box (what I'm currently messing around with) is 2.5 cubic feet double walled (doubled up on mdf so 1.5" walls all around) tuned to 55. The sub is firing into the cabin on the passanger side and the vent which is 72^2 inches is on the drivers side of the box. I am following db drag rules so everythign is sealed up and mic on the windshield. I peaked at 43hz so that tells me the box is tuned too high. I reached a score of 141.0 I then took a piece of mdf the length and height of the box and put it in the vent. This brought the area to be 63^2 inches and the tuning was dropped to 50. I tested and came out with same results. I then upgraded my wiring from 4 gauge all around, to 0 gauge all around i gained .5db's. i have another plug that I will be throwing in the vent monday to drop the tunning to 44. i will then update you guys with the outcome and go from there. I plan on building another box but this time having the sub and the vent firing towards the cabin sealed off from the trunk. I just don't know if I should run a box at 2.5 cubic feet or smaller. i will be using a 6" precision port and start from 30 and cut away until I dont get any more increases. So my question for you guys is what would you recommend 2.5 cubic foot box or smaller?