Originally Posted by eucariote
I find that after some time with a set of headphones (~1 month) the signature becomes very familiar and small differences from that sound become very noticeable. For example I could only hear the most subtle of differences between a Denon D5000 and D7000 but after a few months the differences and relative shortcomings of each headphone was very easy to hear.
Really all learning works like this.
Getting used to the sound signature of a headphone is very important in any case.
Usually when I just received a new headphone it sounds a bit 'meh', and I don't really like the sound signature because it's different from what I'm used to.
After some time however, I start to get used to the sound signature and I'm starting like it more and more, until eventually I might even heavily prefer it over what I had before. Conditioning is a very important factor here, you might even call it 'psychological burn-in'.
Back to the original question of the OP:
A lot of people state that fiddling around with EQ for long times has improved their hearing abilities of subtle differences in the frequency domain, additionally it is supposed to help people identify certain frequencies. I haven't tried this myself, but the fact that I have heard it from countless people seems like significant evidence. Enough to give it a serious try, at least.