Special buy on this killer long excursion passive radiator. High mass for very low tuning so put it in as small of a box as you can that just fits for this and a high excursion 6.5 or 8 inch subwoofer. If using a super long excursion 8 you should use a pair. Now you can tune that tiny box super low and not need a port 10x the size of the box (in other words, impossible) to do it