i have rockford fosgate phase one 12 inch subwoofers 8 of them in a 16 cub ft box im trying to get them to hit low and hard they do hit very hard and loud!! but when the songs go to the low bass it drops out they are ported 6 ports 4inch by 3inch deep the ports are all on the front side with the subwoofers thats what rockford gave to me they say that will tunes them to 37hz but it sounds like they are tuned to high and out put around the 50hz and lower drops off and i dont get that lower end that shakes the car and flexs the car just trying to get my point across on what kind bass looking for please help me

Whew I'm tired after reading that one long sentence.

If that 16 cubic feet is after port and sub displacement, you're tuned to..............wait for it............46 hz. That's your problem.

You need to build a new box. Or at least lengthen the ports to 8". That would lower your tune to around 35 hz and make it a bit more listenable. But it would be hard for me to believe that you don't have port noise with only 75 sq. inches of port for those eight 12s. You may have to redesign a new box to get more port area if you experience noise.