Placement could be the problem.
Sit the sub in the primary listening position and crawl (yes crawl) around the room listening for when the sub sounds good.
Once you find the best spot, put the sub there and then listen from the main listening position.
Hopefully it will sound much better.
Sit the sub in the primary listening position and crawl (yes crawl) around the room listening for when the sub sounds good.
Once you find the best spot, put the sub there and then listen from the main listening position.
Hopefully it will sound much better.