There are many ways to figure out the best place to put subwoofers in a room. Most involve measurement and then interpreting the measurements. But what if you don't have any measuring tools? How do you find the best place to put a subwoofer sans tests, numbers, graphic displays and automatic room correction systems? Easy. Just do the "quick and dirty flip flop." It's even G-rated.
Here's the drill: Put your subwoofer at your primary listening position, hook it up and put on something with bass info. Then walk around your room and stand in the various places where you could put a subwoofer and listen for the quality of the bass. Some spots will have too little bass and some too much. Pick the spot where the bass is most to your liking, and put the subwoofer there. Game over.
Sure, you can run some tests to confirm what your ears are hearing if you wish, but if you go for the quick and dirty flip flop, I guarantee you that you will be quite pleased by the results.