okay, i have a 1000watt sony xlpod sub(XSL120P5A), and a 850watt monoblock(ssl is all i know) amp, my mate has a 600 watt fusion sub and a 450 watt fusion amp, and his thumps way harder than mine, both in sealed boxes,
could be a lot of raesons, really. box specs driver specs amplifier settings amplifier power (max or peak versus RMS) vehicle types and corresponding environmental variables all the rest of your and his system (other than just sub and amp) electrical systems
both of ur guyses systems blow... that xplode will prolly blow soon and ur friends fusion stuff is just terrible.. u got money for a new system? well hook u up bro
my old room mate had 2 fusion 12's on a 320 watt class a/b kicker amp, it dident sound bad for 40$, but the 10" type E i put in my g/f's car was almost as loud on 175 watts. the xplode subs suck there amps have sucked ever senths they fired there r&d team and found out they can just put fugged numbers on there boxes and they will still sell.