I would also add that a very common problem is playing a sub too hard outside it's tuning. It is usually very easy to identify if a sub is labouring, by just watching what the subs are doing, ie. if they are moving alot but the actual sound or output is not as loud as with other songs or frequencies then chances are you are playing the subs out of their tuning or "happy place" lol. Because what is actually happening at that point is that the sub's supension is trying to do all the work, and not getting any or little help from the box, almost the same as taking the sub and putting it on the floor and pounding the same 500 watts to it. A good example of this is competitive spl setups, they have very pointed tuning, in other words they are meant to play a very limited frequency. But when they are playing that frequency or money note, they are in control or a controlled environment if you will, that is why they can take 10,000+ watts each. BUT, if they slipped up and played the wrong note, the result is usually Carnage (don't ask me how I know that). If their note is say 60hz and they played 50hz that could be the result. Hope that helps.
