Originally Posted by AndrewFG
The building is thick concrete, and it would be hard to shake it.
Concrete doesn't make for perfect sound proofing. If you have neighbours on the other side of your concrete walls or floors, I'm sure you've noticed this.
1) A reflection issue? The mic was on the sofa backed against the wall (so the mic was 0.5m from the wall behind, and 3.5m .. 4.0m from the sub...)
2) A standing wave / resonance issue? The room is an open plan L shape with a big chimney place in the middle of one wall; construction is concrete; floor covering is engineered wood with rugs on top.
3) A passive resonance with the main speakers? The FL & FR mains are big (old) B&W Matrixes which go down about 40Hz.
1) This would increase the distance, not shorten it.
2) The sound resonating through the floor, either the concete or the engineered wood, is essentially what kriktsemaj99 is suggesting is causing your problem.
3) The other speakers aren't in use when the subwoofer is being tested.
YPAO is just supposed to set your speaker settings automatically. If gets something wrong and you know the correct value then the solution to your problem is simple. Do what kriktsemaj99 suggested and manually set the correct value.