Yes, there are many speakers that can get to the 30hz range with those 6.5" drivers. VBT has a claimed frequency response of 18hz(-6db) with one of their subs using a 6.5" driver.
There are tradeoff though. A 6.5" driver generally can't play as loud as a 10" driver before breaking up. Second deep bass in small boxes generally means lower effeciency. So yep physics still applys.
There are tradeoff though. A 6.5" driver generally can't play as loud as a 10" driver before breaking up. Second deep bass in small boxes generally means lower effeciency. So yep physics still applys.