While I was modding my X-LS's, I decided to use the No-rez dampening material (similar to Blackhole 5) on my CBM-170SE's instead since they have thinner cabinet walls. So, I proceeded to disassemble my CBM-170s to install the no-rez. I made one mistake - when removing the quick connects from the tweeter, I didn't notice the notched hole holding it in and pulled the whole ounting tab off of my tweeter. One ruined tweeter, a call to Ascend for a new one, a few bucks out of my bank account (stupidity tax), a few days for shipping, and I'm back in business.
Since I had already ruined the tweeter I completed the no-rez install on one speaker while waiting for the new tweeter. I removed the poly batting glied to the sides and cut no-rez to fit the sides, top, back and bottom (the back and bottom were multiple smaller slices to get around the crossover/port/binding post cup). I reassembled the speakers and installed my replacement tweeter today.
I intentionally only did one speaker first to try and compare. I'd have to to some special work to really compare (make audio files/CDs with the same content on both channels), but so far I'm not certain if there's an audible improvement. If I touch the cabinets while their playing, I can't say there's a noticable difference in how much they vibrate (since the change in mass isn't significant, this isn't really surprising).
I'll listen some more before doing the other one before passing final judgement, but right now I'm not certain if I could tell you which was the treated one if you blindfolded me.