How deep should a subwoofer play?
Extension to 20 Hz is not automatically better. Useful bandwidth depends on programme material, room gain, maximum SPL, placement and integration.
Extension versus output
Every extra octave of low-frequency extension demands rapidly increasing displacement if sound pressure is to stay constant. A design can trade enclosure size, driver area, excursion and amplifier power against one another.
Room interaction
Below the room transition region the listening room dominates the response. Boundary gain may extend the low end, while room modes can create peaks and nulls that are much larger than small differences between simulated alignments.
Define the target
For home cinema, strong output in the 20–30 Hz region may be a design priority. Music-only systems may choose a different compromise. The useful target is not one isolated F3 number but a combination of bandwidth, headroom and in-room response.