Just to quote your conclusion part of your post, I agree with that and it fits my experience EQ'ing headphones to the same curve from measurements, so I agree with your post that was tempering some elements of what @tusing was concluding in his post. We can't use frequency response to totally equate the quality of two headphones - eg comparing DCA Stealth to another headphone that can mimic that frequency response. That's where the importance of the subjective review comes in or indeed listening to the headphones yourself. Harman is an excellent step forward, but it's not a done deal for the reasons you mentioned (HPTF variability, HRTF variability & additionally some inherent user measurement inaccuracies that can be associated with chosen measurement methodology (& implementation) to arrive at the final EQ'able measurement e.g. do you use an average of a number of measurements from different headphone reseatings or do you choose just one actual measurement to EQ, etc, and then a last additional point you have unit to unit manufacturing variance as well as pad wear that will alter the frequency response away from any measurement you find on the internet).So while Harman's research tends to give credence that once FR is a controlled variable, provided distortion is low enough, HPs are similarly rated, I'm not certain that FR remains a sufficiently well controlled variable in terms of actual on-head response that it makes questions of "cup reflections and design" not that important.
Fantastic interview with Sean Olive, posted by Audioholics today, describing the methodologies and justifications behind the design of the Harman target. Sean Olive mentions the DCA Stealth and @amirm 's review at 51:20, but it's really just in passing. I'd recommend that people watch the whole video, it's very educational!
One interesting aspect I found is that the Harman target was preferred regardless of cultural background or musical/listening experience - even very experienced listeners almost universally preferred the Harman target.
Another interesting aspect was that experienced listeners were almost completely unable to differentiate between Headphone A equalized to sound like Headphone B, versus just Headphone B (with the rare exception of when either headphone might exhibit a significant amount of distortion.) This implies that cup reflections and design really might not play as big of a role as we like to think, and audiophiles might not be as good at distinguishing non-FR aspects as they like to think.
Sean Olive makes it very clear that you don't need to spend $4K to get a headphone that performs extremely well. A lot of the headphones in the $50-$200 range match the Harman target closely. I'd love to see Amir review some of the headphones in blue:
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It's funny to imagine this graph extending all the way to $4000, running well off of my screen, and a single dot slightly higher than the JBL Tune 710 representing the DCA Stealth. (Didn't stop me from purchasing the Stealth, though!)
The future of headphones will probably be cheap drivers DSP'd to the Harman target, with some degree of head tracking with binaural reproduction, and audiophiles will be at a loss as to what to spend their money on next.
Like a mechanical watch versus a quartz watch, headphones like the Stealth are very much a novelty for the rich, in that what makes them unique is that they don't need DSP to achieve a high preference rating, but that is immaterial to the sound quality in the end. If Olive is right, you should be able to get Stealth levels of performance for a fourtieth of the price.
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