It's affordable to add a sub to your system, versus buying full range. You do not have to spend big bucks to get a sub now. What full range speakers are you referring too? It all depends on your mains, if your speakers are flat down to 20 hertz, you really don't need a sub, unless you listen to some rap or other bass heavy tracks. If you want to get low, you need a sub.
Why the fascination with subwoofers?
I have noticed many posts with questions about adding subwoofers to an audio system. Why the fascination with subwoofers? I guess I understand why any audiophile would want to hear more tight bass in their audio system, but why add a subwoofer to an existing audio system when they don’t always perform well, are costly, and are difficult to integrate with the many varied speakers offered. Additionally, why wouldn’t any audiophile first choose a speaker with a well designed bass driver designed, engineered and BUILT INTO that same cabinet? If anyone’s speakers were not giving enough tight bass, why wouldn’t that person sell those speakers and buy a pair that does have tight bass?