That's not what BASS box pro software shows me. With an active subsonic filter, prior to amplifaction, the SSF (or technicaclly the infrasonic filter) does what you say, true, but also allows the woofer to work in smaller boxes as it no longer is having to work on those frequencies blocked by the filter, kind of like it sees the box as if it were a smaller driver. In some instances, substantially smaller boxes. There are limitations too, but all the same, SSF is always a good idea when you are tuning an octave or two above. Rarely is that not the case with car audio subs. Different story in home theater where a lot of infrasonic material is added to the soundtracks. Hit me up if you ever want an expample, I'll run the numbers and show you the graphs, it's kinda cool.