Can someone explain to me what the freq response rating on subs mean, does it mean it can only play the freq range that its giving or what. Some subs as lanzar opti only goes down to 40 and subs like my alpines are in the 20. Just wondering, I never really knew what its all about. I got to see if there is z chart that shows what all the ratings mean and why it,s good to know when selecting a sub(s)Thanks for some info.