Hi everyone. This is not my first post, but I've been more of a long time lurker than active poster. However, I've had some 7520's for a while so I thought I'd add my opinion.
First, some very brief background info. I'm a musician by profession (instrumentalist), and, although I have a small home studio, I'm not involved in music production as such. The studio is used mostly to record myself for other peoples projects - CD's or whatever. My main use for headphones like the 7520's is for tracking, checking a recording, and for listening to music around the home on my iPod/iPhone.
In addition to being a musician I also have a life long interest in HI-Fi. I won't list all my equipment, but the CD chain is Marantz CD12LE, Mark Levinson 38, ATC 100SL's. 'Phone's wise, I have Senn HD600 and 650 open, Sony 7509HD and 7520 closed. HP amps are Fostex HP-P1 and Lehmann BCL.
I've read the whole thread from the beginning(!) and I agree with the many positive opinions about the 7520. There are a few things which have been mentioned which I would like to comment on. First, the bass! I agree that it didn't sound good straight away - boomy and somewhat uncontrolled was my initial reaction. It has improved tremendously over time though, and although I still find it too much at times it is very recording dependent, so I think it's more a reflection of a particular recording than a fault with the HP. The mids, as has been said many times, are extremely clear and detailed whilst the highs are very extended and smooth. I think starfly has mentioned sibilance a few times. I think I hear the same thing, although not sibilance as such (I don't generally listen to vocal music), but sometimes a slightly unpleasant shouty quality to something like a rim shot for example. The other criticism that I can relate to is the lack of sound stage. Of course any closed back will not have the sound stage of a good open design, but the 7520 seems a bit more 'closed in', for want of a better description, than some others. Let me say that I think these 'criticisms' are only possible when thinking about the 7520 as a proper Hi-Fi headphone; IMO it absolutely excels and exceeds any expectations that one could have considering it's intended purpose and price point.
However, I do have a problem with the 7520, namely the 7509HD! The 7509HD is a headphone which seems to have been largely ignored on Head-Fi and certainly it doesn't seem to be popular here, although some members (Uncle Eric for example) have praised it. I think the frequency response graph for the 7509HD on Headroom might well be responsible for preventing many people from even listening to the 'phone. All I can say is that it shows me that you really can't tell what a HP will sound like from a frequency response graph! The 7509HD is often criticized for a lack of bass, but, although it is certainly rolled off much more than the 7520, it's there(!) and very clear and controlled. The upper mid bass also never gets in the way of mid range clarity, (which I feel it can to some extent sometimes on the 7520) which IMO is even more revealing than the mid range on the 7520. The highs a just as extended and smooth. The one thing which I do hear as better on the 7509HD than the 7520 is a sense of openness and space (the mid range is just incredible!), and yes, sound stage.
Comparing the 7509HD and 7520 is perhaps somewhat irrelevant as the former is no longer available (unless you care to buy one here! http://www.amazon.com/Sony-MDR7509HD-Professional-Headphone/dp/B000HHYZV6), but I thought I'd post my thoughts in case it might help anyone who has the 7509HD who is thinking about getting the 7520.
Overall I feel that the 7520 is probably the better balanced of the two and I'm sure the sound signature would be more appealing to the vast majority of listeners, but personally I find the better sound stage and holographic mid range of the 7509HD to be more satisfying. However, both are great closed back HP's which, apart from their studio application, are particularly good for listening to music without an amp direct from a portable music carrier.
Edit: I can quite believe the story of Abby Road Studios stockpiling the 7520 before it became unavailable in Europe, but, just for everyone's interest, I do know for a fact that Dave Gilmour purchased several pairs for his home studio. Here's part of an email I had from the UK dealer that I purchased mine from:-
'By the way, our rep asked me to pass this on to you. Not sure if you like Pink Floyd, but apparently, David Gilmour purchased 5 pairs of these lovely cans for his studio. :-)'
Edited by Mike F - 12/27/13 at 10:50am