Headphones are electret ..ie have a built in permanent electrostatic charge and are otherwise similar to classic electrostatics..but less costly . Similar type of construction with a panel not a cone. Mine were from a company called Mitchell and Johnson . The effect is slight but noticeable at the mid to high end .. guitars seem to vibrate a little longer, the clicks are clickery, I can distinguish more clearly the accent of a backing singer, .. things I had not noticed ..but once I do ,I can pick them up again on the Sony's or more standard headphones.
I once heard Quad Electrostatics loud speakers , back probably mid 1960 s , and I was absolutely convinced that there was a person behind me talking.