On the topic of old vs new versions... (note: the following are not my own photos) Here are some earlier HD580 drivers: And then here are some later ones: And then here are some HD600 drivers: I've disassembled HD650 before and all HD650 drivers are closer to the style of the HD600 drivers shown above. So yeah, the magnet assembly is a bit different in some HD580s. I've seen HD600 headphones with the same style magnets (gold/brass/copper ring in the middle), which I'm guessing are actually just HD600 shells housing some older/earlier HD580 drivers (didn't disassemble those so I have no idea, I'm just guessing). HD580/600 are interchangeable. Don't think I've measured much difference in FR between the different magnet styles, but I didn't dive that deep into distortion figures. That might be worth investigating if anyone has the time.