Low frequencies are particularly difficult to stop, and require a lot of mass to do so. The suggestions already made regarding checking for poorly sealed places, or the more invasive process of replacing your floor will certainly help. If you do end up replacing the floor, you could use "mass loaded vinyl" as part of your underlayment, preferably isolated from direct coupling (floating floor). It is one of the more effective barriers and means of adding a lot of mass.
Having said all that, to make any major difference is likely going to require a large investment.
Is your main concern getting your room more quiet, or is it that the TV is a distraction (ie when sleeping etc)? If it is the latter, you might consider actually trying to MASK the sound via running a loud fan, or buying one of those devices that puts out some background noise. I have a couple of these units (IIRC around $50 on Amazon) and they are pretty effective at minimizing distractions from distant sound sources.