Bass is not supposed to be fast. If it were it would be treble. Bass has a much longer wavelength than treble or midrange and takes longer to develop. If your sub seems muddy it's probably because it's crossed over to high or turned up too high.
In addition a good sub will increase the size of the soundstage. A sub that can go down to 20hz or below can better produce 27 or 40hz much easier than speakers that go down to 27hz.
In addition a good sub will increase the size of the soundstage. A sub that can go down to 20hz or below can better produce 27 or 40hz much easier than speakers that go down to 27hz.