Whhy Does My Sub Shut Off when i turn up my volume?

I have a Alpine MRP500 •300 watts RMS x 1 at 4 ohms (500 watts RMS x 1 at 2 ohms) a pioneer Subwoofer Pioneer TS-W309D4 •power range: 50-400 watts RMS (200 watts RMS per coil) •peak power handling: 1,400 watts •12" subwoofer with dual 4-ohm voice coils. it was working fine hitting hard then i smelt somthing burning. afterwards i didnt find anything wrong so i started going on but not the subwoofer can hit as hard anymore. and it turns off when turning the volume up? What should i do?