Update: This X13 is incredible. Ive had a bunch of so called subwoofers over the years, including some ive made myself, but ive never really experienced true sub bass until now.
Ive left it with one port open, set to EQ1, for the lowest response curve. If the graphs ive seen are accurate, response is still very flat, but this is not its THX mode.
I watched "Edge of tomorrow" last night. There is a sound track at the very start of this movie that goes lower than ive heard anywhere before. Reviewers say it approaches 10Hz.
The X13 reproduced this at stunning pressure with no audible distortion, although it was scary strong and made me jump for the remote !
My son, two floors up, came running down to the basement thinking there was an earthquake. I swear the single foam plug is working its way out of the port !