You cant hear frequencies as low as 20 Hz, you can only feel it resonate through your bones, that’s why you perceive that there is a subwoofer in the room when you sit on a couch that has butt kickers built in to it. Further this whole argument over this sub or that sub goes below 20 Hz is a nonsense argument, all subs can perform below 20 Hz, a simple oscillator sweep will prove that. What is important is how well a sub performs above 20 HZ because that is where most of the useful action is. What you want is a tight punch in the chest bottom end, not a boomy or tubby performing sub. You used to see these great big ported boxes or elaborate transmition line type subs, which by today’s standard takes up to much real-estate, or is cost prohibitive to build commercially. So what we have are these small boxes with powerful drivers in them that are coupled to gobs of amplifier power in an attempt to overcome the tremendous amounts of distortion created by utilizing such small enclosures. Everyone has this feedback circuit and that correction circuit and so on spouting off all kinds of specifications to promote their respective product, you’ve got your sunfires, velodynes, earthquakes, triads, an endless list of worthy products that for the most part all work quite well. But the problem is, all of them invariably end up stuck in a corner somewhere with little though at all as to how the environment is going to affect the performance of these devices. For the most part all of these subs end up sounding like crap simply because they are installed in the wrong place or the listener is setting in the middle of a null or both. If I were you I would stop worrying about what lies below 20 Hz and be more concerned about whether or not you can even properly perceive anything below 80 Hz at your primary listening position.