Hi, which would be best for placing my subwoofer in the corner of my room (the sub is downward firing): 1. having the air port facing a wall that is a pillar wall (cement pillar with drywall covering), 2. having the air port facing a normal wall (exterior wall...drywall over insulation), 3. having the air port facing the open part of the room towards the listener. 4. rotating the sub so that the speaker is facing the cement/pillar wall with the air port at the other wall or out to the listener.
Nobody can tell you how the sub will perform in your room because it depends on how it interacts with the room. The only way to get the best sound is to experiment with placement. this would include in which direction the port is facing. Bass frequencies are wavelengths that are many times larger then most rooms. So bass has no real direction. The problem is that the way those waves interact with the room can lead to certain areas becoming boomy and other areas to have virtually no bass. The best thing to do is to experiment. I personally like the port facing one of the walls, but some others will say differently.
In other words, you have just got to experiment. Bass is generally non-directional, but placement of the subwoofer will affect the manner of its presentation.