The likelihood is that you will hear a terrible echo. Now try that in your lounge and then go out into the open and try it again. I suppose you get the point. The room walls, the ceiling and the floor all reflect the sound radiated by your speaker. By either increasing or decreasing the amount of reflections you can tailor the sound to suit you.
Lets talk about room factors that affect acoustics.
If you can start with an empty room. You quickly realise that the system is bright, has lots of air and has a rather boomy sound. Throw in a sofa set and things start to change. Throw in rugs, curtains, cupboards etc. If you throw too many things in a room, the room will sound 'dead'.