i have added this sub according to vipermann and was not impressed with the results. i dont think changing the phase of the woofer does anything in this case. With the port installed there is a of of enclosure vibration. I then removed the port and plugged the hole, better but the enclosure still vibrated horribly, after all it is not very rigid. Next i covered the enclosure in dynamat and wow what a difference, eliminate the vibration and the sub sounds 100x better. If you add any sub to this enclosure you have to Dynamat the whole enclosure