The Skullcrushers use tactile sound transducers. TSTs are pretty much identical to the vibrating things found in video game controls. The idea hasn't totally caught on, but TSTs can be applied to car stereos, video game systems, and home theaters (Buttkicker). Tactile sound transducers typically hook up to audio outputs, and, instead of drivers, they use motorized parts which vibrate/spin, usually tuned to move in response to sub bass frequencies. The plus side is that you get the sensation of movement from sub bass frequencies (which we can't hear anyways) without the ear damaging SPLs required to make woofers physically vibrate. The downsides are that they may not be perfectly tuned, or that people see these things as a break from tradition. The idea of applying TSTs to headphones is interesting to me. I have heard the Skullcrushers, and they don't sound very good, but I still sometimes think of adding a set to my collection. Now I just have to decide if I am willing to throw my cred out the window and get Skullcandy, or, even worse, fuss with batteries in my headphones.