I read a post here lately where the poster provided some great advice. Put pillows in the corners and hang blankets on the walls at the first reflection point as a test. Then go from there. No real cost in doing this and then see what happens. Experiment some to see if your room perhaps needs some help.
I tried pillows in the corners and it works nice; just one on the floor worked well and more pillows pilled up did not help further. When I'm done, I just put the pillows back on the sofa and so my cost is in the few moments to move the pillows to or from the corners. I may look at trying the blanket experiment next.