building a sealed box bigger then factory specs is it bad?
 

I have been told from shops that bigger the box the sub well perform better, I prefer sealed boxes cause they sound clean and accurate. I have 2 12" P3 subs in sealed box 1.25 cu ft per chamber, factory specs recommends 1.00 cu ft but shop told me build a bigger box because P3's sound better. Does this only apply to certain subs? I'm building a SQ on my challenger but like little more bass.

If you want more bass then build a vented enclosure and tune it higher. It will be just as clean but will be louder and have deeper bass.

you build a bigger box to go lower ... you build a box too big it will sound like a wet fart.. it all depends what you care about, you want more bass all around (80-20hz) then big sealed with a driver that can handle it.. but the drivers you have perform better in ported I believe so go with Hz advice