what's the down fall of putting a sub in a closet? Let just say you would open the door up when you want to use it? I have a closet that has a passage way underneath the stairs that's just begging to used.
The problem is that there are too many variables to do much reasoning. One could make some guesses, but the way a sub behaves in a particular location depends a lot on the room, the closet, and the sub itself.
When it comes to sub location, you can speculate in a hundred ways and maybe not get close without some missing bit of info. Unless you can model the room accurately along with the response of your sub, which is unlikely with respect to a closet, you just won't know.
My reasoning would be that a closet could present some unique and unexpected interactions and I would simply try it and make some measurements.
There's no general rule concerning closets, it's just the more adjacent surfaces you have to deal with the worse things usually get, and a closet can present other challenges such as creating it's own little echo chamber or even a partial bandpass loading effect on the speaker. In general, placing a speaker inside a chamber like that is a bad idea, although in some cases it probably would be fine.
anyways, the closet looks a bit big to put a sub in... as in id expect the volume of the closet to have a resonant frequency somewhere in a subwoofer's frequency range so probably the closet will work like an untuned bass trap... thats just my hypothesis though