System

I guess what it means is that subs can be much slower than speakers. I had one that could clearly be heard bouncing along behind the music, it was almost comical. In fact I can always hear a slight blurring when a sub is used in a system. A good quality servo driven sub may not be within your budget.
How about some more info on your system, or add a system link to your profile.

This article IMO provides the best description I have seen of what the confusing and seemingly oxymoronic term "fast bass" means.

Regards,
-- Al

I have Triangle speakers and the sub I use is a Velodyne Optimum 8. If you have a large room you might want to look at the 10 or 12. In my small space, the 8 is more than enough.
It's a sealed design that is very fast. It also has a room correcting eq that works very well.