I am experimenting with these DIY basstraps, one in each corner behind the speakers. They do have some kind of influence on the LF, but in what area, I have no clue. The deeper bass seems to wander less back and forth in my listening room though. It's more dry in a way, like the majority of the pressure waves are less noticeable. I have made them with both inner and outer membranes, in order to increase their effectiveness.
I am aware that I need at least two more of these in order to achieve something worth mentioning, but I feel this may be a step in the right direction. And I don't have any more raw material on hand as it is. After all, it's an experiment. At least they're better than what I had earlier.
They are made from foam matresses rolled up very tightly around a plastic membrane, and the bag they are placed in, is more or less airtight. Pretty? No, but fun to play with