Sound leaking on the Sennheiser HD 555's?

Since they're full-sized cans, they probably share characteristics w/ similar sized Sennheiser sets I do own. If they're anything like the HD600, HD650 or HD800, they'll let a LOT of sound out. Not good for quiet surroundings like libraries or even the workplace. Like my sets, they're probably not all that great about keeping sound from getting in either...unless you want to blast your eardrums by cranking up the tunes. Fact is, none of my open back Senns--small or large--have ever been close to decent when it comes to providing ANY amount of sound isolation. My PortaPros aren't great either, but I think surrounding people nearby tend to notice the leakage from them less (smaller drivers, less sonic energy), and I've just gotten used to the external sound infiltration that they allow.

I have a pair, it's basically because they are open back headphones, that piece of metal on the back is all that seperates the speaker cone from the outside, one quick fix Idea that I came up with but haven't put into practice is making some of that -12db foam with sound cancelling foam. (shaped into triangular prisms or something) and mount that around the speaker, but not actually on the cone otherwise you'll get serious rattling...I take back buying these to be honest, they SOUND AMAZING, it's just...if you're listening to something loud cause you like it loud (ME) well...it fails. I really should have bought a pair of sound cancelling ones.