Green Mountain Audio Callisto. 90-91 db effecient, rated at 50 hz, but I sold my sub since they go way lower than that. I listen to all kinds of music, but rock kicks butt on the Callisto's. Best speaker and company for the money and worth much more. Please take the time to hear these before you commit to another speaker. These will change your life.
http://www.6moons.com/audioreviews/gma2/callisto.html
http://www.greenmountainaudio.com/
http://www.6moons.com/audioreviews/gma2/callisto.html
http://www.greenmountainaudio.com/