Extremely late answer,I know, but I actually did this in my room to counter a 27hz mode and it did wonders. Tightened up the bass in the deep and resulted in the feeling of more bass in the sweetspot, while the vibrations from seats were lessened. In my case I used my tower up to 40hz. It was annoyingly hard to hit it right though, due to the lpf making a phase shift, thus rendering the timing of some frequencies off. With a FIR filter it would have been much easier to integrate, as well as work longer up in the frequency band. Here is a couple of measurements showing the impact of this bass cancellation project in the waterfall response. Fwiw i tested the bag end device here at home, and it didn't work that well, it just didn't have the output capability to handle it. This tower was so much better for me in my room.