Speaker manufacturers need to quote frequency range within decibel limits.
If Cabasse quote 41Hz at the bottom end it might be -3dB or -6dB, or worse. Whatever, at the usual rate of roll-off there will be nothing at 20dB. If OP is hearing a significant signal then it might be room effect but more likely check his Dirac.
For those interested bottom B on a Steinway Model 6 is 31Hz. The bottom of a string or electric bass is 41Hz.
Those wishing significant musical output down to 20dB definitely require sub-woofers with these Cabasses. I wonder what instrument they are listening to.