Wid,
Yes the max extension mode is 25Hz, but the VTF2 will still hit 93dB at 20Hz according to Tom Nousaine who test a lot of subs for S&V mag(http://members.cox.net/fabulousfrankie/Nousaine.htm)and thats why I said 20Hz. Just like the VTF3 max extension mode is 20Hz but the VTF3 will still do 88dB at 16Hz.