The walls in our homes keeps us safe and warm, a modern cave protecting us from the outside elements. Playing music within those walls changes how we hear that music, a trumpet played in a small room vs. a large hall sound very different. The same is true for our stereo systems played within our walls.
You would not enjoy the sound of your stereo system if played outside. Sitting in front of the speaker pair in your backyard, the music would be lifeless, robbed of important information supplied not by the speakers, but by the walls themselves. Thus, in any stereo setup we depend on our walls for good sound.
Think about how much time and money you spend getting your electronics perfected, then compare that to what you invest in walls. If you are like me, the ratio is heavily skewed in favor of equipment. I take my walls for granted, now that I have done what I can with them. And yet, these walls are as important as the system itself. Without walls, our sound is dead.
When we spend any time thinking about walls we mostly consider them a hindrance, like a pesky insect that never goes away. Yet, without walls we will never achieve great sound in rooms, just as without insects our world would cease living; though the little pests are still bothersome.
The next time you sit in your living room with the lights low, think about walls.