Edit: I just took one. It's about 92dB to the ratshack meter a few dB below reference. Your guess is as good as mine as to how far off the SPL meter is at 6Hz.
These videos are great. I've got to get someone to host some shots I have of my BP 1803 (LT) during testing at 10 Hz and during the "Jurassic Lunch" segment of the Great Fantasy Adventure test CD. There is nothing like seeing an 18" driver moving over an inch each way!!! JP
I just fired up BHD to that part you guys were talking about. I didn't hear or feel much right off. Just for fun I used a mirror to watch the sub. I was watching at 6dB from reference with no infrasonic filter. The cone was just flapping, you could indeed count the cycles. amazingly it didn't bottom out though, despite being ported at 18hz.
I hadn't noticed the really-really low frequency in BHD, so I fired it up on my IBs (don't use a high-pass filter). Of course I couldn't hear it...it just modulated the room surfaces.
I'll offer a theory that it is the beat frequency of 2 helicopters running at slightly different speeds.
i just caught (the act of marshalling in an aircraft or helicopter, assist in shutting it down, chocking it, grounding it, and other related tasks) 2 blackhawk helicopters over the weekend, and i think the bass in BHD is spot on. one thing i noticed when i launched them, as i was around 30ft away from the tips of the blades, the bass wasn't there during startup or idle, only when they changed the pitch of their blades to lift off the ground did the bass start thumping. i wish i could've got a ride, but they said with the wind we are getting here, that they couldn't have given me a proper ride anyway.