The 2014 Loudspeaker Industry Sourcebook came out this week. In it, you can find an article I wrote called "Perceiving and Measuring Headphone Sound Quality: Do Listeners Agree on What Makes a Headphone Sound Good?"
The article is a summary of some recent published research we've conducted at Harman on the perception and measurement of headphone sound quality.
Together, these studies provide scientific evidence that when headphone brand, price, fashion, and celebrity endorsement are removed subjective evaluations, listeners generally agree on what makes a headphone sound good.
So far, this has been true regardless of users' listening training, age, or culture. The more preferred headphones tend to have a smooth, extended frequency response that approximates an accurate loudspeaker's in-room response. This new target frequency response could provide the basis for a new and improved headphone target response. You can find more details on the research here.