All rooms are boxes. It is good to think of them from “outside the box” to get some control over what is happening to sound. Generally, a small room will have more problems than a large open area as sound reflections will be magnified at the frequencies the box. Small rooms need more treatment as sound will bounce around the room, off the walls and ceiling many more times than a larger room.
Also a square room is more problematic than a rectangular room, as having the walls the same distance apart can create strong “standing waves”. You may have heard that in your room where a particular bass frequency rattles the walls but others do not. If you haven’t, pull out a bass and play the scale and you’ll find it.