What exactly is its difference with the in this forum so much discussed Harman loudspeaker score??
The question wasn't for me and is a hot potato around here. Indeed, conceptually, I'd say that there isn't much difference.
I am not a huge fan of the Harman speaker's score btw, at least as a single parameter.
To qualify this, let me say that there are two FR curves I like, one of them being the Harman one, the other being close to the "secondary" Harman one (the bass boosted one).
All other things being equal, I tend to agree that the Harman curve is mostly my preferred one for general use. But the thing that bothers me when it is used as a single measure of speaker quality is that all other things never seem to be equal... Is it the speaker's design and its interaction with the room? Is it its directivity? Its distortion characteristics? I don't know and that's why I keep reading the loudspeaker's discussions around here.
In my experience - and I have quite a few speakers pairs I can compare side by side without and with equalization - there are often very significant differences other than their FR.
And as far as headphones are concerned, even if I am not a headphone guy (my speaker's spending over the last 10 years or so has been 200 times higher than on headphones), I find those differences even more striking when I use earphones or in-ears. Looking at this list, I realize I own some very highly rated in-ears in terms of correlation with Harman's curve, but that they are essentially trash in terms of resolution, transient response, imaging etc compared to very poorly correlated ones. (I also own the HD-600 which I find quite likable)
Also, one thing that struck me btw is that the current version of Amir seems to strictly go by Harman's curve in current evaluations, but the older version of Amir could not accept that mitchco equalized LS50 + subs were remotely similar to mitchco bigger speakers (and I think we can trust him on EQ). Now, the argument seems to be FR is all what matters, I still don't get why it wasn't the case back then.