Cant get sound

This method will be easier and less time consuming than "crawling for bass." Required equipment needed but not limited to, an SPL meter and test tone generator.

Place your subwoofer firmly where your prime listening position will be, with the driver pointed in an unobstructed direction. It is best to place it exactly in your seating position at or near ear level if possible in whatever manner you deem is safe for you and your equipment. If using a downfiring model placed on a couch, sit on a peice of plywood.

Adjust the volume control as close as possible to where reference level would be at the lowest frequency for your subwoofer model.

Run sweep tone through the sub and measure output on your SPL meter from the possible locations that your subwoofer could be placed in the room. Place the meter as close as possible to where the subwoofer would be, either held in hand or tripod mounted, or any other placement method that does not subject the meter to vibration.
The position with the flatest response is ideal, however, differences in media usage or crossover setup then one may desire a higher output at a given frequency. This method will tell you exactly where to put the sub without having to move it around!