IF you listen at normal/low levels, sound leakage is VERY minimal (with headphones ON of course
). I work in a cubicle environment and when I used my D5000s here at low volumes, no one could hear anything. Now, when I went past let's say 60-70%, it leaked A LOT!!! So definitely the Denons are not Fully closed. It's a fact that has been mentioned quite a few times before and a lot of people sees it as a negative/con. It does not leak like an open headphone but still...
There are a lot of GREAT 'closed' can choices. My favorites would be:
Shure SRH940
Shure SRH840
Ultrasone Signature Pros
Fostex T50RPs -- MrSpeakers Mad Dogs
If I had to live with just one of these... ermmm.. it would definitely be a toss up between the Mad Dogs and the Sig Pros.... just great sound reproduction throughout!