Pics or didn't happen!
Congrats on your dual subs!
I was under the impression you can not hear anything under 20Hz. In fact, I thought being able to hear 20Hz was like having 20/20 vision, not everyone can see that well. Likewise, not everyone can even hear down to 20Hz, let alone below that.
With my PB12-NSD on the Bass I Love You song, I hear deep bass, then a lack of sound but a strong vibration of my couch, room, and house. To the point where my wife, who was upstairs taking a shower, came out and asked what the heck was going on as she felt the house shaking. I believe this is the 17 Hz signal, which apparently my sub is able to produce in my room.