I use Sennheiser HD25s - not noise cancelling, but if I have music on I can hear absolutely nothing going on around me. It's actually a little bit spooky (and

I use Sennheiser HD25s - not noise cancelling, but if I have music on I can hear absolutely nothing going on around me. It's actually a little bit spooky (and often makes me jump) if I'm working and someone comes into the room behind me then comes into my field of vision, or someone taps me on the shoulder...