If you expect a subwoofer to perform optimally it has to be set up correctly. This small fact has not been lost on premium subwoofer manufacturers such as Velodyne and JL Audio. Most of their subwoofers have some kind of built-in "expert system," with automatic calibration to make it easier to install them correctly. But what about subwoofers that don't have any built-in calibration or set-up features? Here's my under ½ hour subwoofer set-up method.
All rooms, regardless of their shape or size, have "room nodes" where bass is augmented or reduced. And how do we discover where all these spots are? We could plug our room dimensions into a chart or computer program that will spit out set of specifications that can tell us what frequencies and room locations could be potential problems, or we could take a more empirical approach, which I call giving the subwoofer "the catbird seat."
For this set-up you do need to be able to place the subwoofer in your primary listening position, and maybe even IN your listening chair. If your subwoofer is especially big or heavy, this may be a two-person job, but the goal is to put the subwoofer as near to the same position as your main listening spot as humanly possible.
Once you have your sub in your favorite listening position you need to hook it up and put a low frequency tones through it. If your system is connected to a computer you could use a test tone suite, such as "AudioTest." I usually use a 40 Hz sine wave as a starting point, then a series of sweeps from 20 Hz to 90 Hz. As the sweeps are playing I walk around the room and listen to them. In some spots the test tones will be much louder than other spots. As I walk around, I spend time listening in the spots where I could possibly put my subwoofer. In some rooms with limited options I'll pick the spot with the most bass reinforcement as the final location for my subwoofer. In spaces with more than one spot with augmented bass, I prefer to choose a subwoofer location that has some, but not too much bass augmentation.
After I've chosen the spot where I think the bass is "best," I disconnect the subwoofer and move it to that location, and reattach it to my system. Then I listen to more test tones (and measure their output levels via an iPhone APP). Again I use sine-wave sweeps, but this time they are more full-range from 20 Hz up to 3000 Hz. The goal now is to get levels where the sub blends well with my mains. I also experiment with the crossover points, usually trying 50, 60, 70, and 80 Hz and then listening for which one will deliver the smoothest and most cohesive hand-off from subwoofer to main speakers.
Usually this whole process takes less than ½ hour and the final results yield a subwoofer location that will work well for all but the most pernicious rooms.