It is just a 1″ topper. Well it is actually 1.25″ but it would be equivalent to most 1″ pads. I worked on the tuning and tuned it to 40hz, which allows me to use some minor eq to get the extension all flat down to 35hz and usable down to 30hz. Without doing any eq, my receiver using audyssey room eq picked it as a 40hz crossover. Meaning that if you are using any room eq, it should do those minor adjustments for you and cross it over low if that is what you desire. And I will say, I really enjoy crossing it over that low.
I didn’t measure the overall sensitivity, but the sensitivity should be the same as a single woofer, which is 98db 1w/1m.