I have a 12 X 15 room that opens in one corner to stairs and another room. Otherwise it is a perfect rectangle. Eight foot ceiling. Due to WAF and layout, I can't move things around. The "front" is on the 12 foot wall. Anyway, i'm curious as to why bass frequencies are the strongest in the middle of the room, towards the ceiling. I sit down (head at three feet) and the bass drops by at least 5 dB and as much as 8 db. (Measured) Mostly in the 50-100 Hz range. Is it typical to have this happen? Like I said, I can't move things or install treatments. I just want to know the physics behind it. However, I do have a spot for a second sub on the opposite end of the room. If that would make a noticeable difference.