In most home theatre systems, the sub-woofer is shoved in a corner or hidden wherever it causes the least aesthetic problems. Interestingly, in most Home Theatre setups, the subwoofer is not where it should be! If the sub is in the correct place you should hear no obvious bass; it should just seamlessly blend in with the surrounding audio but should still be able to pack a punch when needed in those big explosions. It should be smooth and even.
You could spend a bit of money buying an audio reader which you wave around like a wand finding peaks and nulls and and keep moving the sub until the sound level is perfect in your seat. You could spend even more money paying someone else to wave the magic wand and tell you where to put it. If you're anything like me though, you hate spending more money than needed and so there is one final option for you. You can do the "sub-woofer crawl"!
"What is the subwoofer crawl?", I hear you ask... Ah, it's what those magic wand wavers don't want you to know about. Basically, you place the sub-woofer in the spot where your seat is (some lifting required) and while playing back a movie or audio track, you crawl around the room like a goose with your head at your seated listening level and find the place where the bass sounds smooth and even. This sweet spot will not be the loudest bass but the cleanest. There may be a few sweet spots in the one room. Once the place is found, you place the sub-woofer in that spot and return your chair to its position. Sit down, and enjoy the perfect sound.
In each room the best spot for the sub-woofer may not be the nicest looking place so I found it handy to find the places in my room where I could live with the look of it. I then listened specifically in these spots and chose from these. It was amazing where my sweet spots were!
The beauty of this system is that it doesn't cost anything, it will fix any shape room even those with open walls and larger windows, and it will most importantly make your current setup sound its best. You may draw a few questioning looks or even open mocking but that is something I am willing to take if I can improve my system without spending a dollar or even leaving the house!