I’ve only checked pa sub drivers on parts Express that’s probably why I think they don’t go too low . I forgot about port tubing supposedly you can go as low as you require .
Pro subwoofers are capable of some serious powerfully output .
The ones we use for ultra low bass (down to 25Hz) are 6th order bandpass subs, which can manipulate the F3 rolloff point and efficiency, more than other types of enclosures.
The vents inside the enclosure, are slots that are the full width of the cabinet, and at least one of them is over 2 feet (!) long, inside the cabinet. That's how it's tuned that low...
Regards,
Gordon.



