Considering the FR of the Bic F12 is only 25-200hz it is not surprising you do not register anything with a 20 hz tone. I suspect that the 25 hz is already 6db down as per normal spec ratings and things roll off very quickly after that.

The Tempest looks good, nicely done.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70