Right, so the baseline of the Harman target is an in-room measurement of a Revel F208, in the Harman room, which had been equalized to a flat response at the listening position on an omni mic, measured with a GRAS 45CA, right? The original (well, "original" - 2013) Harman target was derived by applying a pair of shelf filters based on listener preferences to that baseline
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This, clearly, generally works rather well, since it's the foundation of the Harman work, which predicts subjective preference well. However, because it's an in-room measurement, to achieve a smooth target, a fairly large amount of smoothing was required (@Sean Olive can correct me if I'm wrong, but people less directly connected have said it's in the 1/2-1/4 octave range). This obscures some finer HRTF features and slightly changes others (such as the shape of the rise into the "ear gain" region).
These small details don't matter as much as the general trend, which of course is why the Harman target is overwhelmingly preferred, bur being able to work with higher resolution data is handy because headphone response measurements typically show features that are much high Q than the in-room measurement's resolution can incorporate. With GRAS fixtures, the "pinna notch" feature around 9khz is the iconic example - B&K gear typically has a constructive (rather than destructive) feature in this same area. It would improve our targets to have these small details included, and with anechoic data, we can get very high resolution HRTFs to work without having room modes or reflections interfering.
So when you talk about "anechoic data" then, I guess you'd be specifically referring to free-field measurements made from different angles on a HATS rig, like the ones shown here?...
That's not overly surprising, given that Theile's work underpins the DF target. However there is a quite substantial difference in sound between FF (a frontally located flat loudspeaker in an anechoic environment) and DF - and indeed attacking FF both on its inaccuracy under his paradigm of reproduction and its subjective non-preferability is what Theile 1986 is about.
Our thinking does seem to run along slightly similar lines, on some things. Imo though, diffuse field curves will only work as a neutral in-ear raw response curve after they've been corrected to better match the sound power response of speakers in a room. Others will probably argue that this is too simplistic an approach. But I think you can probably get a fairly good approximation for a speaker's raw in-ear response on the 5128 rig by simply combining the speaker's diffuse sound power curve with the 5128's diffuse field curve.
This probably won't capture all of the important details in the treble, especially in-between the resonant peaks at about 3, 8 and 16 kHz, as described in one of my other posts above. But I think it'll at least put you somewhere in the ballpark for the peaks in the treble. Which is certainly better than nothin at all. And probably about as good (or maybe even better than?) what the current Harman target can do on a GRAS rig.
Regarding "low frequency boost", I feel like I get into this dialogue about every 5 days at this point, but an anechoically flat loudspeaker's in-room power response doesn't show a Harman-esque bass shelf unless it maintains directivity control to an atypically low frequency, and then rapidly transitions to omnidirectionality. The Revels used track the general 1dB/oct or so slant pretty well without equalization in-room
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but their slant is closer to the "B&K curve". As, of course, there's a degree of circularity in defining speakers as good based on anechoically flat response and power response that yields the preferred in-room power response (would we more prefer a non-anechoically-flat speaker with differing directivity but the same power response?).
Some actual in-room measurements of speakers might resemble the old B&K speaker curve. It is not as good a match though to the estimated in-room response curves of well-extended speakers in the currently available spinorama data though. Which tends to be a bit more withdrawn, rather than more forward in the midrange frequencies. And also more steeply sloped upward towards the lower frequencies, before the curve begins to roll off in the sub-bass.
With the 5128 DF + sound power approach that I've been talkin about though (probably ad nauseum at this point), you can use whatever response you want for the sound power curve. Including the SP response of a "grot-box", if that's what you like or need for your work. It's really entirely up to you. And if you wanted to do something similar for the GRAS, then you could use an approach like Robbo is doing with the in-room curves instead... There is more than one way of skinning a cat, as they say. And they're just different ways of arriving at a similar result imho.
If you have some other ideas on how to go about something like this though, in addition to measuring some actual speakers in a typical room (which is somethin I can't do, since I don't have a 5128 rig), I'd be interested to hear some of them.
Based on the spinorama data I've seen though (which is admittedly somewhat sparse in this particular area), I think the bass/sub-bass response on the current Harman target is probably not too far away from the sub-bass response of a loudspeaker that has a flat direct/on-axis response which is very well extended into the sub-bass frequencies using either calibration and/or a built-in sub. Or perhaps a separate sub-woofer. And that seems to be what Dr. Olive was sayin here as well.
That type of well-extend response obviously won't be everyone's listening preference though as a model for a headphone's response. So it's nice to have some other options available imo. Particularly for open dynamic headphones.
The impacts of shoulders are less than you might think in an environment with reflections, but yes, I believe the 43AG used in an earlier paper was placed in a mannequin for specifically this reason.
Good to know. (ASR doesn't seem to have a thumbs up icon, but that would go here.)
I'm unsure what "the other steps above" are, in this case - if you're referring to the Harman work in the period where in room measurements were being done (e.g. Listener Preferences for Different Headphone Target Response Curves and Listener Preferences for In-Room Loudspeaker and Headphone Target Responses), IMO the initial flattening of the speaker in situ response serves an interesting function in showing that the preferred EQ adjustments for both headphones and speakers are similar - that is, that preferred headphone frequency response and speaker power response are roughly equivalent.
Fwiw, I agree that in the context of the study they were doing, that it was interesting to see the room curve and the flattened speaker's in-ear response separated.
If you just want to see or measure the speaker's normal bass-biased in-room response at the ear, then there should be no need to separate its "room gain" from the rest of its (in-ear) response. Because you could just measure the speaker "as is" (with no EQ applied) to get its in-ear equivalent. To do something like that though, you'd probably need either a fairly expensive pair of fullrange speakers that are already well-extended in the sub-bass frequencies (if that's what you want to emulate). Or maybe a separate sub (or possibly some EQ) to accomplish the same thing, as Dr. Olive noted.
I guess it's possible that an approach like the one Harman used, with the flattened and separated in-room and in-ear responses might be easier for some folks though. (?)
I did try to re-edit my previous post on this, btw, to try to make it a bit more clear. But maybe the context was/is just too confusing to make sense of those remarks.
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