The magic in my setting offers a lot of control, at the expense of energy equivalent to whatever the task you're doing. So, lifting a 5 pound box is equally as difficult with magic as it would be in real life, energy consumption wise. This hasn't been a problem yet, but it's raised some questions of energy cost for various spells - Specifically, how much energy would it take to create a really loud noise, in the most efficient way possible? Or, more generally, what is the most efficient way to create a really loud noise, all other circumstances being variable? An explosion? A sonic boom created by throwing something really, really fast?