Bass is a strange creature. I was running a small 8" sub that only went down to 40hz, but wanted more bass, so I bought another 8" sub.
At the listening position, the bass was softer like I was in a vacuum, but as I walked out towards the edge or stood up, the bass was booming hard! Poor neighbors.
I learned the second sub activated standing waves and nulls and achieved the opposite of what I wanted. I went to one properly positioned bigger sub and now life is good again.