For a quick good time, blankets...

I used to drape an old army wool blanket over my TV flat screen since it sits between my speakers and it does make an improvement but I've gotten so lazy that I stopped doing it. The trick is to not overdo it. Case in point: I replaced an overstuffed sofa with some lounge chairs and the sound improved noticeably from the mids on down to the bass. I would never have sold my old speakers had I replaced that sofa first. You never know until you try.

All the best,
Nonoise

Well, I'm not necessarily suggesting a permanent installation, but I forget sometimes how much you can learn about your system without spending any money.

Trying out pillows and blankets or throw rugs can be revealing for no cost. :)

Best,

E

erik, if you have the speakers on hardwood or tile floors, any kind of sound absorption in front and between them on the floor is an absolute requirement. Also, depending on the speaker type, some absorption (or defraction) on the ceilings between/front the speakers will improve the SQ. This is all about removing unwanted floor/ceiling reflections and having them mixed with the direct sound from the speakers as they reach our ears at different times, etc. But you probably knew all this already.