Properly integrating a sub is really hard work, and rarely done by 90% of those who buy a subwoofer.
Technically, correct! I would even go as high as 100%. But 90 will do. Which is why I always and only recommend a DBA with 4 subs. Try and do it with just one and you are doomed to failure. When even the guy who uses one knows it is really hard work, and even then works only rarely, everyone should listen.
And then go out and get more subs. To do it right.