Measuring it with a high output impedance allows the cans to be as undamped as possible and lets the phase swing more easily for a strong response when measured. Since all the cans are measured similarly, it allows for better relative evaluation.
Birgir and Kevin have done us all a solid, and I'm gonna need some help getting electrostatic cans in for measurement.
Really the easiest way to tell you about it is just to point you here:
Looking forward to a bunch of new estat measurements!
Thanks Birgir and Kevin! Imma make good use out of the KGSSSRE.
Just to clarify, I use eq regularly for personal enjoyment...mostly on the AK240 as most of my personal headphone listening ends up being portable. (If I'm home and listening, I'm working.) But I don't use EQ for review work as I want to review the headphones themselves.