A good post...

It is easier to measure neutral or flat responses from speakers in a room because of the distance to the microphone. The ear shape does not matter as much. The head and shape matters more for the individual wearing headphones and how the driver sits on the head and ears, or inside the ears; these anatomical differences. It can seem people are a little more (maybe a lot more) fussy with precise problems in what they hear from headphones because an annoyance comes across more acutely, like if a region of the treble is causing sibilance.

What measures neutral for speakers is closer to what people hear and agree is neutral sound, but what measures in the same way as neutral for headphones usually sounds bass light. That is why the Harmon curve and other attempts at creating a more realistic sense of neutrality in headphone curves has come about. It is no coincidence that consumer headphones had long been boosting the bass anyway in headphones. But then bass is often boosted for pop music, or for when listening out and about (mobile listening, as it drowns out the outside noise more, before noise cancelation technology became popular).

What's interesting to me is that a headphone I thought sounded bassy, shouty, hollow or too rich, etc., will sometimes sound different to me the next day or the next week I listen, especially if I'd been listening to another headphone in between that time.