You'll probably want to equalize and DSP would be the ideal way to do so. Virtually all bass speakers require equalization (unless they're either refrigerator sized or are also tuned to not go very loud) so F3 becomes a somewhat arbitrary choice made in the active filter that powered subs have onboard. As an 18" speaker, this one can move a fair about of air so dialing in a 20Hz knee is suitable. As an unpowered speaker we'll do this in the upstream of our external amplifier. The best way is to taper down the response above that desired point; say, 25Hz. Asking room correction to do is probably best because it includes local acoustical gain in its final filter function. Specifying a maximum output between 20Hz and 30Hz is a fairly common indicator - it shows us the speaker's ceiling along its lowest likely response knee. The average peak specification reflects the maximum excursion and the voice coil's thermal or wattage limit, which are reasonably close together. Max output is naturally less at 20Hz than at 30Hz, hence the average.