If you click on the link you'll see that the left cup has that large chip the right cup doesn't. It takes up a significant portion of the cup and would definitely effect acoustics. So the left and right cups are not the same.
As I stated before, the cups of the 940 and 840 are very similar.
Also, I've mentioned that I believe the major sound difference between the 940 and 840 is the bass. I think it effects the entire balance and sound signature. The internal construction of the two headphones are very similar. So, I'm guessing the drivers are tuned differently.