Wow, I guess it's not that common, sorry I didn't give more info. I stumbled across a couple of posts a few months back (I forget where...I can't find the posts anymore) which suggested exactly that...shooting, or industrial hearing protection worn over the IEMs in particularly noisy environments (i.e. planes & trains). The claim was that it was at least as effective as active noise cancelling, which obviously is a different animal to begin with. ANC always has some influence on the SQ, so at the least I thought it was a fairly good idea to minimize excessive volume when traveling. I wasn't sure if that extra seal would negate the ADEL benefits. I actually don't travel that often, but I was intrigued by the idea, and since my experience on planes is that bass does diminish due to the background noise, I thought I'd ask. I usually keep the volume at a reasonable level, so unless I'm using bass heavy earphones, my listening experience can suffer. Thanks for the response!