I was playing with a audio test DVD this morning and I heard some distortion when the sweep got down to 20htz. I have a super cube 3 from Def Tech, and I know that these subs don't go very low. So I was curious if I had damaged my sub. How would I know if I blew it out? Is it possible to blow it out? Wouldn't the sub just stop responding if the signal was to low for it to play? My volume was around -20, which I believe is about 85dbl on my system.