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did you ever go with the HD650's?

I have a pair of these that I used to use at work, though I'm currently using a set of HD280pro.

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I was wondering how much sound bleeds out from them when listening to them at a fair volume.

Some, but not too much -- I never had any complaints from my cube mate about it, anyway. But then, they've always been on my head, so I can't really say anything from first-hand experience.

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Also, how much outside noise bleeds in? I was interested in using them to block out noise from my office, and listen to music while i work. I thought the open air (aside from sounding really good and "natural") would help me hear someone calling me while working, or the phone, etc. I don’t want to totally block everything out.

They do not work at all for blocking outside noise. They overpower outside noise (depending on the volume level you're listening at), giving you something more coherent to focus on, instead of the standard office environment noises. The open back design definitely allows you to hear what's going on. Frequently, I'd just mute the music, and have a conversation with someone, without ever removing the headphones.

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What do you think of them for use in an office with people close by.

I like them, and will probably go back to them, once I figure out which box I put them in. They're certainly the most comfortable pair of headphones I've worn, so I highly recommend them if you're going to be wearing them for 8 hours a day -- well worth the price. They're a solid set of headphones that have, so far, withstood nearly daily use for a couple of use -- by contrast, my HD280s, after less than a year of use, are being held together with packing tape.

Edit: Sorry... I have the HD600, not the HD650. They're pretty much the same in terms of the open-back design, though, so what I say above should still apply.