Home Theater Questions? Ask a Technician for Answers ASAP
What is the Brand and Model of the subwoofer, ad also of the receiver?
How long have you owned it for and when did the problem occur?
ANY details at all that you can give me will help you sort this problem. I've been installing and repairing AV equipment for over 25 years. Let me know if you need help.
If you're simply looking for general information, then a typical subwoofer will have thumpy bass either caused by a setting on the subwoofer (the crossover is turned up higher than usual), the same could also be true on the surround receiver (which is why I asked what receiver you have), or in the case of an older subwoofer, the physical suspension of the subwoofer itself (the surround around the cone and the spider underneath the code) have stretch out and are no longer compliant, allowing the woofer to be "loose" and not retain the bass tightness it once had.
Feel free to reply back if you need more help, or want to reply back with more details. It does not cost you anything more to reply back once you've rated. Please do rate me positively (at least 3 STARS) and I will continue with you until this is sorted. The positive rating ensures I am credited for my work.