Here are the measurements of the Sennheiser HD 660 S2 on the B&K 5128. For our target we use Diffuse Field with an 8dB slope applied to match listener preference research.
Raw
Compensated
HD 660 S2 vs HD 600 (both with fresh pads)
Channel Matching
Here’s an initial EQ profile done subjectively. I don’t think I can fix the 4.5khz dip as that seems to be a deep phase cancellation issue, but… I’m not really that fussed since it’s fairly narrow.
And here’s the result with these changes.
My take at the moment is that the HD 660 S2 is very similar to the HD 600 and HD 650, just with a more relaxed tuning in the upper mids. So for those who found the other two to be a bit shouty, the HD 660 S2 will be a good alternative. Personally I still prefer the HD 600 and HD 650.