I've noticed that my back "subs" aren't really working that well? I don't really receive any bass from them at all (i put my hand over it and little to no air comes out, especially with bass heavy songs).

I NEVER have my music really loud, (In fact, I've only had my music at max like, twice, to test how loud it actually really was) so I don't think I could ever pop or blow them.

Any suggestions?