Changing Hz range in car audio

What do you mean?

well some subwoofer systems push at around 28 HZ and i want to get it to 30 Hz. the amp iam usin has a low frequency responce of 20 Hz and i want to know if i can change that to 30 Hz by wirring the amp or the speakers different. my amp is a rockford fastgate T2001bd with (3) 15 inch rockford fasgate P3D415 and i have the amp bridged down to one OHM......hope this is enough info

If it goes down to 20Hz, you should be able to play 30Hz just fine. Subwoofers aren't supposed to play just a single tone- just like all other speakers, they play whatever tone the amplifier sends them.