I would think an Anchor of some sort was used, as the frame of every axiom speaker consists of MDF...
I know I recently put up a shelf in the garage, screwing the shelf supports into MDF...I knew in the pit of my stomach that it wouldn't hold over time with all the weight on there (wasn't much, a bunch of boxes from the speakers, and a kick drum hard case that weighs around 15 pounds mabey).
Well, it lasted for about a week, and I came into the garage and found 2 of the freaking supports ripped right out of the MDF...
Needless to say, I have since used some drywall anchors (good for 30 lbs of weight each) for each support (2 for each support) behind the MDF...nothing has crashed...yet
I know you can buy some pretty hefty anchors...but do you REALLY want to drill holes in your M80s?!?!?!
