On Tue, 05 Sep 2006 13:19:30 +0100, Peter Spikings
wrote:

Hi all,

I'd like to start listening to music at work but
sometimes it can get pretty quiet and I don't want to
disturb anyone else. I've looked into it and seen that
you can get headphones which attempt to cancel out noise
but they stop external sound getting in and don't seem
to try and stop their own generated sound from getting
out, what I want is pretty much the reverse, i.e. I want
to avoid disturbing others around me but want to know
when someone comes up behind me and starts talking

In sound theory, there is something called the reciprocity law. As applied
to your situation, it means that any headphones that let you hear others
will radiate some reproduced sound.

You could obtain the effect you desire by mixing the output of a micophone
into the music that you are listening to, and using tightly-sealed
headphones, perhaps IEMs.