What exactly does "fast" mean? ... lack of bloated bass notes or boomyness? This is a term used so frequently here like rhythm and pace. I don't know why a sub needs to be fast if it's only driving the bottom octave. How would such a speaker "keep up" with high frequency drivers in a main speaker? And would a smaller woofer be more able to to this than a larger one? As stated above, I use the ULD18 and it keeps up quite well with the Maggie 3.3, but then again, how would I know that it did not?
I think the purpose here is to set the frequency in the sub low enough so it does not drive the vocals or other critical frequencies that the main speakers are more optimized to do. And then to adjust the sub's level so that it does not make a presence in the room except for those occasions where bottom octave material exists.
Driving your main speakers full range still taxes the main amp to cover the low frequencies in the main speakers that the sub can much better do. So running main speakers full range causes you to lose in most cases, the biggest advantage of having a sub in the first place.
I think the purpose here is to set the frequency in the sub low enough so it does not drive the vocals or other critical frequencies that the main speakers are more optimized to do. And then to adjust the sub's level so that it does not make a presence in the room except for those occasions where bottom octave material exists.
Driving your main speakers full range still taxes the main amp to cover the low frequencies in the main speakers that the sub can much better do. So running main speakers full range causes you to lose in most cases, the biggest advantage of having a sub in the first place.