Try to actually listen to subs and not just buy by specs. Subs sound different. Port noise, THD, cabinet vibration, driver speed, sealed design, etc. all make up a sub's sound. Take something you are familiar with that has two quick back to back bass notes or explosions. Are they being reproduced as two separate notes or are you getting one long note because the driver doesn't have the transient speed to start stop and start stop again that quickly? The battle in chapter 4 of Master and Commander is a good example, once things get going can you hear multiple cannon shots or one long rumble of varing loudness of vague cannon shots? You'll find even different model subs within a brand tuned the same way will sound different.