Yep, that's the the RS SPL meter said. Using a Fluke DMM to monitor the frequency. Had it dialed in to 20.03 Hz.
Willd already made of fun of me, but I'm telling you... the cone was really movin'! Just a few minutes ago, set the frequency to 13 Hz and cranked the gain until the clip light on the amp just started to flicker. SPL meter read an even 100 dB. Using a spreadsheet I got over at the HT Shack, that should be around 112 dB corrected. Feels like a freakin' helicopter is landing on top of my house.
Man, this is a lot of fun!
Edit: Got a solid 99 dB uncorrected on the meter at 12.5 Hz with the amp near clipping (one channel, 750W max). Again, about 112 dB corrected. If I moved the meter toward the corner of the room, hit 103 uncorrected. Stick it 10 inches in front of the port and it read 112 dB uncorrected! Also noticing an odd smell coming out of the subwoofer. Maybe fumes from the 3M adhesive or the latex calk or... ??