I know that in general the transient response of sealed subs are supposed to be better than that of ported subs and ported subs are supposed to have quite a bit more output at the lower end. But the output seems very similar between the FV15Hp and the F25 and the F25 should have better transient response than the FV15HP. According to the Rythmik website:

"Output comparison

At 20 Hz, our subs vary in their maximum output capability. The output at 20 Hz is shown relative to F12.

F12: 0db (baseline)
F15: +2db D15: +2db
LV12R: +2.5db
E15HP: + 3.5db
F15HP: +4db
FV15: +7db
FV15HP: +9.5db
F25: +8db"

So the FV15HP has a slight advantage of output at 20Hz. However, since the F25 is sealed it should roll off more gradually, so below 20Hz output should be higher on the F25. If the differences in output are only slight, will I hear much of a difference between the two with music? What about with movies? If a sealed sub has the same output capability as a similarly priced ported sub, wouldn't the sealed sub be the better of the two?

I compared my new Sierra 2s with other similarly priced speakers exhibiting flat frequency response on axis as well as quite far off axis. I could immediately hear the difference between the Sierra 2s and the other speakers and I attribute this mostly to the faster transient response of the ribbon tweeter in the Sierra 2s. A better comparison is the folks that have upgraded the Sierra 1 to the Sierra 2 and preferred the difference in sound quality for almost double the price. I wonder if the same will hold true in the below 80 Hz region with subwoofers?