David, It all depends on your room and the type of speakers you have.
For primary reflections over 200 Hz acoustic tiles work great and are dirt cheap. https://www.parts-express.com/sonic-barrier-fwp122-studio-acoustic-foam-wedge-panel-12-x-12-x-2-black-12-pack--260-547
You can find your primary reflection points using the mirror method then place these tiles at those points. Your image will solidify.
Dealing with bass is far more complicated. The best way is to use multiple subwoofers.
For primary reflections over 200 Hz acoustic tiles work great and are dirt cheap. https://www.parts-express.com/sonic-barrier-fwp122-studio-acoustic-foam-wedge-panel-12-x-12-x-2-black-12-pack--260-547
You can find your primary reflection points using the mirror method then place these tiles at those points. Your image will solidify.
Dealing with bass is far more complicated. The best way is to use multiple subwoofers.