Quiet JBL Amp

I've got a jbp bp300.1 connected to a mtx 8000 10" dvc wired to 2 ohm. Also installed is an alpine 3548 which drive my mids with 80 W rms per channel (2 speakers in parrallel, 40 W per speaker). The problem is that my sub is really really quiet. With the alpine's sensitivity turned down to min and the jbl's turned to max, with full bass boost, the bass is only barely loud enough to match the volume of the mids. I used to power the sub with a phoenix gold 2 channel amp that gave it 175 rms, and it's sensitivity had to be turned up fairly high as well, but not all the way and it didn't need any bass boost.

Any ideas why the jbl is so quiet?

Thanks

Connect only one voice coil on the sub and have a listen, then try the other one and have a listen. You may have a bad voice coil or a out of phase problem.

I have a jvc sx980 deck... one pair forward, one pair rear outputs. I have a lowish quality rca cable from one pair of the outputs into the trunk, where each channel is split with a y-cable and one line goes to the alpine, one to the jbl.

I'll check the voice coils.