Lots of bass at walls, lack of bass in center of room/listening position


I guess this is relatively common in listening system. Is there any way to smooth this out so I get more bass energy at my listening position? This happens with our without my 2x 18 inch subs. Room is 12 x 16 x 8 ft, speakers 4.5 ft apart on long axis and I am sitting 4.5 feet away. I tried moving back and forward but the entire middle center of the room except near the walls has decreased bass.
Is this a boundary effect or could it be due to bass cancellation effects?
smodtactical
i’ve had the EXACT same issue w huge dip at 80-100hz by mandated listening position. completely solved w a smaller driver(very fast) sub. The b&w db1 is a true system changer. it will play at 80-90hz without any detection issues. i place it just inside left speaker. it has several phase choices which are very easy to hear allowing perfect match w mains. in my room 270 degrees is the correct setting for me. neither 0 or 180 worked well. try it as you will be overwhelmed at the seamless integration.