My older REL Britannia B1 wasn't hard at all since it was set very low to run with full range speakers. And it has plenty of adjustments for fine tuning. Other subs have been a bit more difficult.
I'm now close to a DBA person with three sealed SVS subs doing a very good job in my room. But, for one single seating position, I'm not positive they top the B1 set properly on its own.