Are Sennheisers known to have noticeable left:right balance/EQ differences?
I've bought two pairs of HD558s and they both have the same problem: the sound seems slightly panned to the right. It's not an artifact of me or my setup as it also affects mono tracks, the shift swaps if I turn the headphones around and wear them backwards, and it doesn't happen with other headphones.
I haven't encountered that problem on Sennheisers (or any other headphone brand).
That said, 75% of the time I use Sennheisers, it's my own HD600, or the HD650, HD800, etc, when I attend audio events, and these headphones are more likely to have matched drivers - ie, they test each driver pair to see if the performance variance is minimal. So admittedly, that would be kind of like if I said, "the VW gruppe makes great cars!" but in reality, I own an RS6 and have done test drives on the 911 Turbo and R8, with only very brief drives on the Golf when I helped an older coworker buy a reliable but still fun car for his kid (and he doesn't trust the kid's initial choice of buying a 1980s Firebird with his own savings, because that car screams shenanigans).
Bumming around the web I found a post by some random guy who claims that Sennheiser deliberately uses different EQ on each driver to enhance the overall soundstage. This would go a ways to explain why I notice the problem more on female vocals than other stuff, but I don't know enough about Sennheiser to know if it's a legit statement or bull****.
I have no idea how the hell they can even (continue to) use EQ on a passive headphone that has no circuits, not even a passive circuit with capacitors, to "EQ" the sound on that, much less do a different profile on each earcup.
Even the rationale for it doesn't make any sense. If left and right have enough of a response, and in this case, even an output level variance, it will
not help imaging. It will in fact do the opposite.
Whoever said that, and assuming you did not misunderstand what he was saying,
stop listening to that guy and relegate your imagination of what he looks like to be something like the image below, because uneven output is
not an inside job, and really only the HD800 and the new Orpheus come with a "birth certificate."
This would go a ways to explain why I notice the problem more on female vocals than other stuff
There's bound to be some variance in the response of each driver, which is why on the more expensive headphones they driver match them, including when you buy replacement drivers.
That said, even without such care being taken, the variance should not be too obvious as to pan the image of where the vocals are. There's probably a bad batch and your second set came from that same botched batch from the factory.
