I'm writing this from the office and listening to music with my LZR 588 on the lowest setting.
It seals well, sound stays in and office noise stays out. However, from about medium volume in quiet offices up to about 1/2 to 1 m away, you can hear that someone is listening to music, but more as a vague "Hmm, is that really music or is it my imagination" and not "Hey, someone is listening to metal/bachata/hard rock/salsa/hip hop/R'n'B/whatever". At full volume, you could safely put your headphones down around your neck and you'd get a relatively loud sound.
Personally, I usually only listen at the lowest level in the office, but I could certainly turn it up to medium (which I do as soon as I leave the office).