3db's is very noticeable. Dont forget to add another 3 when you double the power. If you are running 1 10 with 250 watts at 4ohms and you wire in a second to get 500 watts at 2ohms it is a 3db increase for cone area and 3db for x2 the power.
ya how does that work i dont really getthat if i was running a 12" w6v2 and 2 12" w6v2 same conditions same rms to each sub how much of a diffrence would it be i hope you dont say 3 dbs cause that sux what would be the point of spending all of that extra cash for 3 dbs just my 2cents
as james said adding a speaker from one to two adds 3 db but if you stay with the same amp power thats all you would get but double the power you were using to power one now you get another 3 db....this is why the question how loud is loud enough is a good one and how well did i research my results instead of just adding another subwoofer and more power....figure it this way one sub takes up less room and half the power and saves you cash not to mention doing your research gets you the sound quality and increased spl you wnated by going the add more subs and amp way