I kind of summed it up already, the pointing of a subwoofer down a long hallway to give the sound wave longer to travel, so the deepest notes can be heard. I don't have equipment to measure exactly how deep the note and its undertone/overtone series is, but I do know how deep my subs can respond, and that's 16Hz (the guy with the 16ft room's servo subs respond all the way down to 5Hz, where his pre-pro stops responding first). 16Hz requires 21.46 Meters (Calculation from
http://www.sengpielaudio.com/calculator-waves.htm) to complete a wavelength. Therefore, to hear the tone without hearing what's left of it after decay and the likelihood of it running into itself on rebound (standing wave), I need to be standing or sitting at least that distance away from the source of the sound. That means I have to be standing or sitting 70 feet away for an unaltered 16Hz full wave to reach my ears.
So why is it I can hear it in the 16 foot room? Two reasons: his subs point only forward, mine have passive drivers on the side that are pressure-coupled to the primary driver. When I purchased them, that sounded like a really great idea - fill the room with bass. What I didn't realize is that I was also more than tripling the possibility for standing waves, which eats bass. Thus, more sound waves are completing in his room, even if they have to bounce a couple times to do it. Think dumping one rock in a puddle of water versus six. Which one gives you perfect ripples? The second reason is because his subs are larger. They move more air. They also respond equally well at 5Hz and 100Hz, because the servo has to complete the same amount of travel no matter how fast it's moving. Magnetic moving coil moves as far as it can given the amount of power, and as such, at lower power, moves less. Therefore, my subs do not respond with the same amount of volume or strength at 16Hz as they do at 20, 40, or 80. Finally, the ability for the servos to do that makes the walls shake in the room, making the note more noticeable.
None of this has anything to do with headphones, however. At least, not until someone comes up with a servo-driven headphone woofer.