Acoustically perfect rooms are actually the opposite of a square and have no wall parallel to another wall. This is because you want to minimize reverb and capture the sound as it is made. Next time you're in a well designed theater look around and you will notice no parallel walls. In recording studios the walls may seem like they are parallel but really what you see are fake walls with angled walls behind them. The reverb from small ceramic rooms, such as a bathrooms, is nice and deepens the sound which is why it sounds pleasant.