Hi brucek, thats a good question.
I was experimenting to see how far down my two towers would go. From what I could tell each will go down to a good 35 Hz. I was trying it to see if having a two speakers going down that low would help my nulls in the 40 Hz and 70 Hz range. If that was the case I would have assigned my receiver to set speakers as small and crossover at 40 Hz, which is as low as it can go. As you can see, it didn't go so well.
Also, as an update to my previous post, the measurements were taken with a tripod, with an RS meter (.cal loaded in REW), at ear height, at main seating position 11 feet back from front wall.