Hi Danimaz
I have an HSU VTF-3 MK4, since 2010. It came with a test disc containing a true 16hz pipe organ signal from Saint Seans pardon the spelling. It has two ports and can be plugged or just one at a time. The Q adjustment can vary if you want the so called fast sub but really just either extends the low end or not. Subs don't do transients. It has snap and is well damped. It performs very well considering the price. If you are not a novice, I am sure you can tune it in correctly for both your speakers and your room. 2 of them would blow out your windows if you wanted. Save your money and try HSU you won't be disappointed. If you want very fine and money isn't an object try Bag End.