I used Sony headphones many years ago as my primary “cans” until they basically wore out from extreme use. As I like to try different products I moved on to check out various other phones, but always felt the Sony’s were above average in terms of clarity.
The MDR-7509HD stereo headphones have been around for a while, and are well-regarded by those into headphones, so I was interested in checking them out. They’re ready to go out of the box: no cord to attach, 1/4" adapter already screwed in . . . plug ’n’ play. And, they retain the same level of comfort as the somewhat older, but still current MDR-7506.
Tonally, Sony headphones have a particular character to me—high in mid/upper mid clarity, light on bass. Classical music sounds fine on these phones, because they’re like putting the midrange under a magnifying glass (not a microscope, thankfully), and much classical music tends not to have a lot of low-end energy anyway. They’re also excellent phones for tracking, because the level of midrange detail makes it very easy to hear what’s going on in the mix (especially if you’re singing your head off, or playing a guitar solo). And, they can handle very high power levels.
However, for bass-heavy genres like rock and rap, I wouldn’t feel confident that I was placing the bass accurately until I felt I had truly “learned” the phones. I know lots of people who love their Sonys for listening to music, but our task here is to examine the sound in the context of mixing. In that respect, I would consider the MDR- 7509HD as more of a general-purpose set of monitoring headphones than a set optimized specifically for mixing.