Acoustic Boards and Bass Traps make a difference?

[blushiz]

I find it hard to believe that a flat board and a square thing placed in a room could make a difference in sound quality. I mean, I understand how sound waves reflect off walls and stuff, but how can an object at another part of the room help the sound when the sound reaches your ear the same time it reaches the acoustic panel? How exactly do these things work? I just can't comprehend it.