Well, I will be getting my PR in a couple of days that I ordered from Kyle at acoustic-visions.com, but I don't know how much mass to add to it. So here's the setup: I built the 95L Shiva + PR design provided on Adire's site, but I ended up getting the PE 12" DVC instead of the Shiva. This is because I didn't want to wait until March to get my sub up and running! I've also heard that these two subs are quite similar. So, how much mass should I add to the Adire 15" passive radiator for the best overall sound? I wish I knew how to figure this out myself, but I'm sure one of you "experts" could help me out much quicker! Thanks a lot!