He talks about constructive damping built into the room, twin Sheetrock walls with a damping layer in between, and absorptive springs behind being one example, as being the only way to add "good LF damping" into a room. I always assumed my carpet was doing an ok job of LF damping but I guess that was naive.
He also mentions things like room gain doesn't exist. Corner loading doesn't actually add extra output in the LF, we all hear that boundary loading can give extra "free output", Geddes mentions it excites room modes and it does add energy above the "modal region", which I assume is around 300hz and below, so it just seems like we get extra output in the LF range. Just an interesting point.