I'm still looking at subwoofers and was wondering how important the frequency response is. In particular on the low end. My friend has a Sony sub that goes down to 20Hz. The ones I'm looking at don't go down that low, but they seem to be better quality subs. Can someone enlighten me on this aspect of subs and what I should look for. Also, what about the high end? How high should it go since I haven't really looked at that in my research.