I wonder whether what you are sensing at these VLFs is really a harmonic?
I can't hear sinewaves below about 22Hz (probably age related) but I can feel lower frequencies down to about 15Hz as pressure using the 16-46.
Below that point I'm obviously not getting enough dBs to be able to feel anything. The 16-46 response falls off a cliff at 15Hz but can still badly rattles the old windows down to 12Hz. I haven't tried going lower because of the racket from the windows even on a fraction of a second of sinewave.
The IB can make the boarded roof creak and the the doors flex half an inch each way! It managed 120dB easily at several feet uncorrected on the RS meter with hardly any cone movement visible. It made me nauseous at 10 feet while I was browsing! Oddly it still doesn't have the same physiological effects at VLFs as the cylinder. Which is what makes me think there are few harmonics with the IB to cause them. It is a harmonic one feels rather than the fundamental with VLFs.
I've just bought Blackhawk down today so I'll see how your scene behaves using each sub.
