The Fifth Element

Back in the day audiophiles used to throw up carpet or curtains on the wall behind the speakers. Cheap, sometimes ugly, but effective. :P

Domestic audio rooms are sometimes loaded with bad sounding reflected energy which cancels out frequencies, blurs some and creates in general false information to your music playback.
Luck may have it that some rooms are naturally in better shape than others thus leaving most of the work to speaker placement and attention to a clean soundfield (don't put turntables in front of woofers etc).
But other rooms may benefit from sound absorption discretely placed where it kills room reverb.
My current listening room can not tolerate sonex panels up front but a rear wall is out of the sight lines and calling for damping material.
And I wasn't in need of front curtains but they would help a lot up front with killing secondary reflections so in they go.
The well considered purchase of competent lively audio components is half the challenge in getting high quality playback.
The room is the other half.
Considering a good basic system costs over 20 grand the least an intelligent soul could do is spend a few shekels on getting the room to help the sound.
Common sense.