Assuming the speed of sound (lots of variables here, but let's pick a number), to be around 1130 feet per second (fps), we can find the wavelength in feet by dividing the speed of sound by the frequency. So, 1130fps / 20Hz = 56.5 feet. Close enough for our discussion.
We know that the average room isn't large enough for a wavelength of 56.5 feet to fully develop. What happens is as the wavelength being reproduced becomes longer than the dimensions of the room, the pressure in the room increases. Higher frequencies allow the pressure wave being reproduced (say, 100Hz at 11.3 feet long), to dominate what we hear. But as we decrease the frequency (80Hz = 14.3ft., 60Hz = 18.83ft., 30Hz = 37.67ft. etc.), the pressure wave is overcome by the pressurization of the room itself 80, 60,or 30 times each second. This is commonly refered to as room gain, or room lift.
Typically, upstairs rooms present the worst case scenario as sound pressure is lost in all directions. That's why upstairs rooms have trouble supporting pressurization below a certain frequency. Yet, go down stairs and the bass will often seem deeper and stronger than upstairs.
When you're looking for deep and powerful bass, realize that at some point depending on your room, you're no longer dealing with a wavelength, but a pressurization of the room so many times each second. Getting the amplitude of those room pressurizations equal at all frequencies, and proportionate to the rest of the frequencies being reproduced at your listening position is often an exercise in frustration.
Headphones work on the same principal. Pressurize the ear canal 20 times per second and we percieve that we're hearing 20Hz.
Hope this helps.
