HBK Headphone Measurement Talks from Head-Fi and Sean Olive

[Deleted member 16543]

Small variations in capsule placement and the head's alignment can produce narrow variations in HRTF because, of course, that is how we hear - it's why Middlebrooks' methodology was interesting, he largely controlled for that with simultaneous multi-point measurements (which, again, did not find anything at 3-6khz...). From the paper whose figure includes the 3khz effect in discussion, I point you to the conclusion that the actual authors came to, which parallels my own on the subject:
View attachment 158362
Fairly extreme precision in measurements must be demonstrated under Baffless' method to ensure that we are not just "measuring noise" with his variations, and to my knowledge this has not been done. If you'd like to, that would be a service to science.

This is a relatively significant impact to attribute to a hitherto-undocumented directional impact on acoustic Z. Again, it could be, but your conjecture here far outstrips the evidence available, and the field consensus here is that the canal is directionally invariant.


All measurements used in the Harman study are on a 45CA, at its ear simulators. Measurements at that point are called "DRP", standing for Drum Reference Point, because the acoustic parameters of the HATS or ear simulator match the SPL at, you guessed it, a human eardrum. If you need evidence of this, I recommend reading the pertinent IEC and ITU-T standards (60318-7 and P57/P58).

If your contention here is that the selection of test fixture to measure headphones for the Harman research is arbitrary and unrelated to the behavior in real human ears, someone should probably tell poor Todd Welti.

Again, 12-14 kHz is audible and good enough to justify a completely anthropomorphic canal.

As for the 3-6 range, I think the models should describe observations, and not the other way around. You ascribe all of these observations to errors in positioning the equipment.
I think there may be a little bit of a 'spherical cow' factor at play.
I guess more research would be needed. Real measurements with the method used by Baffless, but validated in lab like conditions, with laser accuracy placements, to see who's right.

 

[ADU]

I think the K701 have flat pads though don't they? I know of course the K702 have angled pads. (Ha, I don't want to accept they're the same headphone!)

I'm a little unclear on this as well. The Q701 that Tyll reviewed definitely had the angled pads. And it appeared to me that the K701 did as well. But I'm not sure about that. I also don't know what the differences between the K701 and K702 would be. If you normalize the two curves somewhere in the midrange though, then it looks like the 702 might be a little better extended in the bass, and a bit brighter in the upper mids.

It does seem strange that the bass levels are different, as you'd think bass measurements would be least affected by different choice of ear design, but of course it's obvious that the same target curve can't be used between the two measurement rigs (which is what's been done in this slide, but I don't think you're referring to that point specifically). I caught a snippet of your earlier posts where you postulated that seal might be compromised on the less uniform sealing surface of the B&K 5128 vs the flat surface of the GRAS 45CA - seems likely however the swivel mechanism of the cups on the K702/701 are very flexible and can move freely in all dimensions to allow for optimal angular contact with the surface, but it's still easier to imagine a better seal being achieved on the GRAS 45CA. Perhaps size/depth of outer ear makes a difference if they are different in spec - for instance it seems the closer the driver is to the outer ear then the more bass you get, as seen in worn pad vs fresh pad K702 measurements where thinner pads = more response below 1kHz (or less treble depending on how you look at it)......so perhaps if the B&K outer ear protrudes less from the head ("less deep") then therefore the outer ear is further away from the driver and therefore perhaps less bass, just an idea.

Appreciate your insights on the above, Robbo. Especially regarding the the swivel and seal on the K701. Your comments on the thinner pads jibes with my experience on AKG K553 as well. This may not apply to all headphone designs, but thinner pads on those AKG's with the large pads seems to mean a little more warmth (or a bit less treble?) than a thicker pad.

I'm not not sure why the ear on the HBK 5128 would protrude less than the ears on the GRAS 45CA though. That doesn't quite make sense to me.

Also, I can't take the credit for coming up with the theory regarding the different potential leakages on a flat plate vs. the more curvy/bumpy surface of a mannikin head. I believe that idea has been around for some time. At least since Tyll's been doing measurements on his Head Acoustics system with a mannikin head. And others having been doing flat plate measurements. And I think this was also one of Dr. Olive's theories for some of the differences in this study, based on his comments here, and also here.

It seems a plausible enough idea though, to explain at least some (though maybe not all) of the differences in the bass measurements on the 5128 and GRAS 45CA rigs, just based on looking at the designs of the two different devices. And based on some of my experiences and difficulties getting a headphone like the AKG K553 to seal well on my own (somewhat bumpy) head.

I believe the debate re flat vs. more rounded and anthropomorphic surfaces has been an ongoing one in the headphone measurement community though. As indicated by some of the other comments here on this subject. And suspect we will also be hearing more from the researchers at Harman on this as well (based on some of Dr. Olive's recent comments).

 

[ADU]

I'd love to see a bit more investigation done on the effect of the geometry around the pinna indeed, which in the case of test rigs, and perhaps even the KEMAR, don't look to me superbly anatomically correct.
Not just in terms of seal, but also in terms of front volume "volume", earcup angle relative the ears, and pad compression evenness.

Fwiw, I agree that this is maybe something that could/should be looked at a bit closer, Maya.

Something else which could also potentially effect the seal of a headphone on a real human head vs a simulator is perhaps the amount of sweat, moisture, and oil on the skin. I don't know how closely this has been looked at, but maybe adding a little moisture between the surface of the rig and pads might help some headphones seal a bit better on a mannikin head. Or maybe there are some different kinds of surfaces that could be used to cover the head and areas around the ear which could do a better job of simulating that. (?)

Some of this could also possibly come down to the skill, experience, adeptness, and insights of the rig operator though. And their ability to preview the effects of the headphone's positioning and seal before the measurements are made.

I posted these old videos in another recent discussion on the difficulties of doing good driver symmetry measurements. But it seems like they might have some relevance here as well...

 

[ADU]

Another question I'll throw out to anyone who may care to respond is-- what do subject listening tests have to do with accuracy?

I can understand the need and value of subjective listening tests when it comes to a typical listener's preferences. But I'd be curious to hear some opinions on why you think they may be necessary, or even useful in achieving greater accuracy.

Maybe this is the wrong question to be asking though. And I should be asking instead whether such a thing as "accuracy" or "neutrality" or "transparency" is even possible in a headphone. Because these are the kinds of words and phrases that I've heard the folks at Harman use in reference to both their products (like the K371) and their research into a target headphone response curve.

And I'm just sort of wondering what they, and others think is the correlation there to the listening tests.

 

[Mad_Economist]

Another question I'll throw out to anyone who may care to respond is-- what do subject listening tests have to do with accuracy?

I can understand the need and value of subjective listening tests when it comes to listener preferences. But I'd curious to hear some opinions I why you think they may be necessary, or even useful in achieving greater accuracy.

Maybe this is the wrong question to be asking though. And I should be asking instead whether such a think as "accuracy" or "neutrality" or "transparency" is even possible in a headphone. These are all words I have heard the folks at Harman use in describing their products (like K371) in reference to their research though. So I'm just sort of wondering what they, and others think is the correlation there.

In my view, "accuracy" in the stereo paradigm is pretty much limited to reproducing the event at some mastering console somewhere. For binaural recordings, we can achieve an acoustic and subjective result equivalent to the person listening to a headphone being at the same position as the binaural recording head, and the work of Gunther Thiele in this area leads me to the position that in this capacity diffuse field is most accurate.

For the Harman work, "accuracy" is in reference to people's perception of the sound as being "accurate" or "uncoloured" as best as I understand it (@Sean Olive, your thoughts?), related to the long-running theme of "closing the circle of confusion". It's not accuracy in the sense of being accurate to an acoustic event - because, in part, there is no original acoustic event - but rather matching people's expectations of subjective timbre.

 

[ADU]

For the Harman work, "accuracy" is in reference to people's perception of the sound as being "accurate" or "uncoloured" as best as I understand it (@Sean Olive, your thoughts?), related to the long-running theme of "closing the circle of confusion". It's not accuracy in the sense of being accurate to an acoustic event - because, in part, there is no original acoustic event - but rather matching people's expectations of subjective timbre.

Fwiw, here is a video where they discuss precisely some of what you describe above, Mad_Economist. I have some theories on this myself, but I'm still having a little trouble understanding how and why they believe that subjective listening tests relate to things like "accuracy" and transparency, or lack of coloration. Unless they are only interested in people's subjective impressions of those things, as you suggest above.

This was posted on AKG's YouTube channel btw. So view it in that context. And I have cued the video to where they begin to make the above remarks. But you should listen to the whole video to understand the context of the remarks better.

 

[Mad_Economist]

Fwiw, here is a video where they discuss precisely some of what you describe above, Mad_Economist. I have some theories on this myself, but I'm still having a little trouble understanding how and why they believe that subjective listening tests relate to things like "accuracy" and transparency, or lack of coloration. Unless they are only interested in people's subjective impressions of those things, as you suggest above.

This was posted on AKG's YouTube channel btw. So view it in that context. I have cued the video to where they begin to make the above remarks.

I mean, what else is there for accuracy when there is nothing to be accurate to? You can, of course, reproduce the sound of being in a given mixing or mastering chair with something like Smyth's realizer (if you can get access to the room), but is that what people are thinking of when they say accurate? Or is it a subjective perception of a lack of colouration?

 

[ADU]

In my view, "accuracy" in the stereo paradigm is pretty much limited to reproducing the event at some mastering console somewhere. For binaural recordings, we can achieve an acoustic and subjective result equivalent to the person listening to a headphone being at the same position as the binaural recording head, and the work of Gunther Thiele in this area leads me to the position that in this capacity diffuse field is most accurate.

You said it. I did not. But I happen to agree that a rig's response to a diffuse sound field can potentially be at least one good starting or reference point to better answering some of these questions.

There are a couple potential problems that I see though with this idea. And the first problem is that there are various different models for a diffuse sound field. So how do you decide which one is the best or most correct?... That might bring us back to the subjective testing again. And Harman actually did some tests with a few different diffuse field models in some of their early work on developing a target headphone response curve. And found that most of them tested pretty low on the subjective tests.

One thing that they did not test though is a diffuse sound field which has been corrected to better match the darker timbre, tilt, tonal balance, whatever, of speakers in a typical semi-reflective room. Which is a very important point imo (and something that we now also have a wealth of data on, thanks to the Klippel other anechoic spinorama measurements done by this and other speaker measurement sites).

The second problem is the accuracy of the DF measurements. Because often the operators of these measurement rigs will make their own custom tweaks or modifications to the pinna and other equipment, which can potentially change their responses away from the factory default DF measurements, leading to inaccuracies in the DF compensation of the measurements on those rigs. This is one of the issues I seem to be encountering with at least some of the GRAS-based headphone measurements.

Based on the discussions here, and elsewhere on the subject of leakage and coupling, I think you could also add these into the mix as well. Because if there are problems getting the headphones to produce a consistent and reliable seal and response, that will also impact the efficacy of any target based on a diffuse model. Just as it would with any other model based on a fixed frequency response curve. Like the Harman target, for example.

The answer to the first problem is relatively simple imo. Because you can (imho) simply take the rig's response to a spectrally flat diffuse field, and then apply a correction to that data to better approximate the somewhat darker overall tonal balance of a speaker's steady state response in a semi-reflective room. It seems to me that this is precisely the kind of thing that Harman's spinorama loudspeaker data was designed for. And that a speaker's overall diffuse response in a room measured at the listening position (which is represented on a spinorama graph by the sound power curve), or something pretty close to it, is probably the appropriate tool or equivalent for this job.

Imo, this is approximated fairly well by a slope in the -1.0 to -1.5 dB per octave range. With maybe a few tweaks here and there to compensate for the directivity and other imperfections, limitations, etc. in a speaker's design.

The accuracy of the DF measurements is also not that complicated. Assuming the factory did the DF measurements well and correctly to begin with, then you just don't make any custom tweaks to the pinna or other gear, so that their response stays much better in sync with the factory's DF measurements for the rig. (The rig manufacturer has to do a good job on the DF measurements in the first place though.)

Another option is to have a rig measured for its DF response by another reputable independent source that does that kind of thing. This would also (potentially) solve the problems related to any customization done on the rig that might alter its response from the factory's default configuration and measurements.

The third problem of consistency in the measurements is just one that the measurement operator is going to have to figure out in consultation with the rig manufacturer. Maybe some tweaks could be necessary to the rig to ensure a better and more consistent response and measurements. In which case, it might need to be re-measured again for its DF response by either the manufacturer or another source.

 

[m8o]

Bulk of time was spent showing and ridiculing the DIY measurement rigs members of his own forum had created. He showed pictures of them and while correctly stating some issues with them, I just could not figure out what he is after. Hobbyist are creating these measurements because headphone companies are not providing them. If Jude wanted to improve things, he should have complained about lack of such measurements from that sector which would be likely to be in this conference, than DIY people. I personally admired the work and creativity people had put in building their various fixtures.

This keeps popping into my head. My hope is my posting of this comment will appease my demons that keep popping this observation and commentary back into my head almost daily.

Well said. I too really appreciate the work of hobbiests using whatever is available to them to measure headphones and fill the void of emperically derived response curves. Caveat being the testing outcomes of their test rig is understood to only be comparable to other tests on the same rig ... but better tests be done of commonly tested headphones and results compared to those made on pro test rigs and an error differential be developed and applied to the results of one's personal tests on their home made rig. This is what I have done and still do. Disappointed it would be poo pooed with a seemingly gleeful superiority.

 

[ADU]

I agree, m8o, that it would be nice to be able to incorporate this type of independent work as well.

This has already been mentioned by others here, but I think another good and potentially much better starting point than using DF curves for answering some of these overall accuracy/neutrality/transparency questions is to do some actual in-ear measurements of the steady-state responses of stereo speakers in a typical semi-reflective room. Both these and also the DF measurements have to be done with a mannikin, btw, to incorporate the head and torso effects on the sound field in the room.

I'm sure someone will correct me if I'm wrong on this. But I believe this is the type of in-room setup that Harman's spinorama speaker measurements were intended to model and approximate from the position of a listener in such a room. The only part that they "left out" though of these spinorama measurements were the effects of the head, torso and ear. Which is what the mannikin and ear simulator would give us.

 

[ADU]

I suspect that most of the participants in this discussion have already seen these. But for those who may be less familiar with the concepts of spinorama and sound power loudspeaker measurements, here are a couple videos of Dr. Toole discussing some of these things in a presentation for some music and audio students, and recently with Erin of Erin's Audio Corner, to perhaps bring you a little more up to speed on some of this.

The only sound power responses we would probably be concerned with as a model of a neutral headphone response, are generally speaking the SP responses of neutral loudspeakers, with a very flat direct response. (And that is the only type of SP data that I personally have been looking at and trying to apply in my 5128 target response curves.)

 

[Sean Olive]

In my view, "accuracy" in the stereo paradigm is pretty much limited to reproducing the event at some mastering console somewhere. For binaural recordings, we can achieve an acoustic and subjective result equivalent to the person listening to a headphone being at the same position as the binaural recording head, and the work of Gunther Thiele in this area leads me to the position that in this capacity diffuse field is most accurate.

For the Harman work, "accuracy" is in reference to people's perception of the sound as being "accurate" or "uncoloured" as best as I understand it (@Sean Olive, your thoughts?), related to the long-running theme of "closing the circle of confusion". It's not accuracy in the sense of being accurate to an acoustic event - because, in part, there is no original acoustic event - but rather matching people's expectations of subjective timbre.

Yes, you can compare binaural measurements of a sound field made at the DRP vs those made during playback to determine accuracy. However, perceptually they may not be equivalent even though the measurements suggest they are. For example, the tactile aspect experienced insitu is missing during playback, and listeners may feel there is less bass in the headphones. This was documented in one of our AES papers on effects of wholebody vibration on bass preference. https://www.aes.org/e-lib/browse.cfm?elib=15150

In terms of reproduction of binaural spatial content content, this recent study at Facebook Reality Labs found that an individualized flat headphone target curve was best, whereas for stereo material listeners preferred the Harman Target Curve. So Thiele's DF target seems to be less ideal for stereo material although it maybe more ideal for binaural. Our BRIR work in automotive audio would suggest that headphones with flat bass may be not ideal.

AES E-Library » Listener-Preferred Headphone Frequency Response for Stereo and Spatial Audio Content

When spatial audio content is presented over headphones, the audio signal is typically filtered with binaural room impulse responses (BRIRs). An accurate virtual auditory space presentation can be achieved by flattening the headphones' frequency response. However, when presenting stereo music...

www.aes.org

In terms of measuring "accuracy" for stereo reproduction via loudspeakers or headphones, I would agree that it's near impossible to objectively determine what is accurate because there is no reference of the playback conditions (headphones or loudspeakers) for most recordings. That leads us to the Circle of Confusion Conundrum, which can only be solved via better standardization in the professional and consumer audio industries.

We don't measure accuracy per se but either fidelity or preference. We train listeners to identify various audio artifacts, expose them in listening tests to a wide distribution of loudspeaker/headphones in terms of sound quality and they learn what is neutral and colored and tend to prefer more neutral. This is generally confirmed by via measurements of the products where listener preference is correlated to the frequency response of a headphone or loudspeaker, and the more linear the measurements are the more they are preferred.

 

[DualTriode]

Small variations in capsule placement and the head's alignment can produce narrow variations in HRTF because, of course, that is how we hear - it's why Middlebrooks' methodology was interesting, he largely controlled for that with simultaneous multi-point measurements (which, again, did not find anything at 3-6khz...). From the paper whose figure includes the 3khz effect in discussion, I point you to the conclusion that the actual authors came to, which parallels my own on the subject:
View attachment 158362
Fairly extreme precision in measurements must be demonstrated under Baffless' method to ensure that we are not just "measuring noise" with his variations, and to my knowledge this has not been done. If you'd like to, that would be a service to science.

This is a relatively significant impact to attribute to a hitherto-undocumented directional impact on acoustic Z. Again, it could be, but your conjecture here far outstrips the evidence available, and the field consensus here is that the canal is directionally invariant.


All measurements used in the Harman study are on a 45CA, at its ear simulators. Measurements at that point are called "DRP", standing for Drum Reference Point, because the acoustic parameters of the HATS or ear simulator match the SPL at, you guessed it, a human eardrum. If you need evidence of this, I recommend reading the pertinent IEC and ITU-T standards (60318-7 and P57/P58).

If your contention here is that the selection of test fixture to measure headphones for the Harman research is arbitrary and unrelated to the behavior in real human ears, someone should probably tell poor Todd Welti.

Hello.

Thank you, I have reread and digested the Harman papers and Hearing-aid international standards. Much or most of this is focused on the function of the human ear and the SLP at the ear drum, or the DRP. You seem not to give credit for knowing that. As it turns we are using hearing aid technology to measure headphones.

To develop the Harman target curve, Harman put headphones on many test subject heads. The test DRP was the test subjects very own ear drums. This is a psychophysics scaling technique not an actual measurement of the SPL. The specific, if it was measured, SPL at the test subject DRP is unimportant as long as the test subject’s response is consistent over multiple test iterations.

Now you have a box of test headphones, recorded sound test tracks and human preference data.

If we were starting from scratch we could use our box of test headphones, recorded sound test tracks and human preference data to develop a target curve for the current GRAS 45 CA-10, the HATS 5128 or some other test fixture. We could even use the older version JBL Modified GRAS 45 test fixture to develop a target curve. Each curve is specific to its own test fixture.

The goal is to develop a target curve that will accurately reflect the preferences of the human test subjects.

Harman reported their results at r = .86 with p < .05.

I expect that some test fixtures may perform better than others.

Thanks DT

 

[Mad_Economist]

The only sound power responses we would probably be concerned with as a model of a neutral headphone response, are generally speaking the SP responses of neutral loudspeakers, with a very flat direct response. (And that is the only type of SP data that I personally have been looking at and trying to apply in my 5128 target response curves.)

Have you seen Chris Struck's paper on deriving in-room eardrum response from HRTFs, room acoustic parameters, and speaker directivity? I made a spreadsheet including the Harman room data at one point, I believe @Robbo99999 has it still.

Yes, you can compare binaural measurements of a sound field made at the DRP vs those made during playback to determine accuracy. However, perceptually they made not be equivalent even though the measurements suggest they are. For example, the tactile aspect experienced insitu is missing during playback, and listeners may feel there is less bass in the headphones. This was documented in one of our AES papers on effects of wholebody vibration https://www.aes.org/e-lib/browse.cfm?elib=15150

In terms of reproduction of binaural spatial content content, this recent study at Facebook Reality Labs found that an individualized flat headphone target curve was best, whereas for stereo material listeners preferred the Harman Target Curve. So Thiele's DF target definitely does not apply to stereo material although it maybe closer to binaural. Our BRIR paper from the automotive work would still indicate that the accuracy of the bass may still not be optimal.

Thank you Dr. Olive. I believe that Theile's position as of 2016 is that the DF target with preferential adjustments matching your adjustments to the in-room baseline of the Harman studies would be preferable for normal stereo content - that is, that the Harman target is correct

In terms of measuring "accuracy" for stereo reproduction via loudspeakers or headphones, I would agree that it's near impossible to objectively determine what is accurate because there is no reference of the playback conditions (headphones or loudspeakers) for most recordings. That leads us to the Circle of Confusion Conundrum, which can only be solved via better standardization in the professional and consumer audio industries.

We don't measure accuracy per se but either fidelity or preference. We train listeners to identify various audio artifacts, expose them in listening tests to a wide distribution of loudspeaker/headphones in terms of sound quality and they learn what is neutral and colored and tend to prefer more neutral. This is generally confirmed by via measurements of the products where listener preference is correlated to the frequency response of a headphone or loudspeaker, and the more linear the measurements are the more they are preferred.

Thank you for the clarification - this is pretty much how I've been explaining it to folks when the Harman work comes up, do you mind if the bolded section is quoted as a single-line explanation of the Harman headphone target work?

 

[Robbo99999]

Have you seen Chris Struck's paper on deriving in-room eardrum response from HRTFs, room acoustic parameters, and speaker directivity? I made a spreadsheet including the Harman room data at one point, I believe @Robbo99999 has it still.


Thank you Dr. Olive. I believe that Theile's position as of 2016 is that the DF target with preferential adjustments matching your adjustments to the in-room baseline of the Harman studies would be preferable for normal stereo content - that is, that the Harman target is correct


Thank you for the clarification - this is pretty much how I've been explaining it to folks when the Harman work comes up, do you mind if the bolded section is quoted as a single-line explanation of the Harman headphone target work?

Hi, yes, I've still got that spreadsheet, attached! (@ADU )

 

[platimn]

Not to seem shrill... but there is really nobody who has an HE-1 Orpheus or is even interested in temporarily obtaining one in a professional capacity other than the paid or "sponsored" reviewers? The only real evidence that I can find of anyone owning one is a dealer claiming to be selling his personal unit in Australia, and a few random comments about how somebody knows some ultra-rich people in China who own a couple between them. Has nobody gone so far as to make an inquiry into a purchase? To obtain the very best in technology in any particular field is often not really possible, but here it seems doable, yet maybe that is just a mirage. It's just funny to me as someone from a visual background, you cannot feasibly get the best in display technology unless you are worth hundreds of millions or represent purchasing power of about as much, yet the best in audio reproduction can be had for the price of a used car.

 

[ADU]

Yes, you can compare binaural measurements of a sound field made at the DRP vs those made during playback to determine accuracy. However, perceptually they made not be equivalent even though the measurements suggest they are. For example, the tactile aspect experienced insitu is missing during playback, and listeners may feel there is less bass in the headphones. This was documented in one of our AES papers on effects of wholebody vibration https://www.aes.org/e-lib/browse.cfm?elib=15150

Thank you for your post above, Dr. Olive.

I'd like to see more good spinorama type measurements of well-extended speakers with either separate or built-in sub-woofers. Because there aren't really enough at the moment to draw precise conclusion on all of this. As I've previously tried to point out though (both here, and now also here), based on the spinorama data that is currently available, I see no appreciable differences between your preferred in-room loudspeaker curve or PIRL (and the current Harman over-ear headphone targets based to some extent on this), and the estimated in-room responses of some of the best extended speakers in the sub-bass, which also have a reasonably flat/neutral on-axis response...

Dutch & Dutch 8C: https://pierreaubert.github.io/spinorama/Dutch Dutch 8C/ErinsAudioCorner/index_eac.html
KEF Reference 5: https://pierreaubert.github.io/spinorama/KEF Reference 5/KEF/index_vendor.html
Infinity Prelude MTS: https://pierreaubert.github.io/spinorama/Infinity Prelude MTS/Infinity/index_vendor.html
Mesanovic RTM10: https://pierreaubert.github.io/spinorama/Mesanovic RTM10/Mesanovic/index_vendor.html
Infinity Intermezzo 4.1t: https://pierreaubert.github.io/spinorama/Infinity Intermezzo 4.1t/Infinity/index_vendor.html

All that suggests to me is that people prefer the sound of really good speakers, that are either well-extended into the sub-bass due to an on-board sub-woofer and/or calibration. Or accompanied by a good standalone sub (or subs). Given the recent proliferation of home theaters with these kinds of setups, I suppose this sort of preference isn't really that surprising. If you feel the need to attribute this to something else (like an absence of tactility), then so be it I guess. But I really see no necessity for that, based on looking at the estimated in-room measurements of these kinds of speakers. The measurements of the two seem to be tracking pretty well, without any other explanations.

All of the speakers in the above links are better extended in the sub-bass than the Revel F208 used for some of your headphone tests...

Revel F208 (ASR measurement V2): https://pierreaubert.github.io/spinorama/Revel F208/ASR/index_asr-v2-20210519.html
Revel F208 (ASR measurement V1): https://pierreaubert.github.io/spinorama/Revel F208/ASR/index_asr-v1-20200508.html
Revel F208 (Revel measurement) https://pierreaubert.github.io/spinorama/Revel F208/Revel/index_vendor.html

And they are also pretty flat and linear in their direct/on-axis response. So they would all fall into the "neutral" category imo.

They are probably pretty close to the top of the heap in terms of their extension into the lower frequencies though. And just to be totally fair, most of the measurements shown above were created by the vendors (including Harman in the case of the Infinitys), rather than other independent sources (such as ASR or Erin's Audio Corner). And the Infinity Intermezzo 4.1t does "cheat" the direct response up a bit in the sub-bass. And the KEF (which has an unusually linear off-axis response) also appears to be tilted a bit more in favor of the lower frequencies.

The better extended a speaker is in the sub-bass though, the better it seems to track with the more elevated levels in the sub-bass in your target response curves for both loudspeakers and headphones. So as already mentioned, I don't see much need beyond this to better explain the levels of the preferred response curves in that range.

 

[ADU]

Harman's preferred in-room curve is the red curve on the right in this diagram, btw. This was previously posted by Dr. Olive here.

Compare that red curve to the in-room responses of the F208 (which is also shown below in light blue), and to the in-room responses of some of the other better-extended speakers shown in the links in my previous post above.

 

[Sean Olive]

Have you seen Chris Struck's paper on deriving in-room eardrum response from HRTFs, room acoustic parameters, and speaker directivity? I made a spreadsheet including the Harman room data at one point, I believe @Robbo99999 has it still.


Thank you Dr. Olive. I believe that Theile's position as of 2016 is that the DF target with preferential adjustments matching your adjustments to the in-room baseline of the Harman studies would be preferable for normal stereo content - that is, that the Harman target is correct


Thank you for the clarification - this is pretty much how I've been explaining it to folks when the Harman work comes up, do you mind if the bolded section is quoted as a single-line explanation of the Harman headphone target work?

Hello.

Thank you, I have reread and digested the Harman papers and Hearing-aid international standards. Much or most of this is focused on the function of the human ear and the SLP at the ear drum, or the DRP. You seem not to give credit for knowing that. As it turns we are using hearing aid technology to measure headphones.

To develop the Harman target curve, Harman put headphones on many test subject heads. The test DRP was the test subjects very own ear drums. This is a psychophysics scaling technique not an actual measurement of the SPL. The specific, if it was measured, SPL at the test subject DRP is unimportant as long as the test subject’s response is consistent over multiple test iterations.

Now you have a box of test headphones, recorded sound test tracks and human preference data.

If we were starting from scratch we could use our box of test headphones, recorded sound test tracks and human preference data to develop a target curve for the current GRAS 45 CA-10, the HATS 5128 or some other test fixture. We could even use the older version JBL Modified GRAS 45 test fixture to develop a target curve. Each curve is specific to its own test fixture.

The goal is to develop a target curve that will accurately reflect the preferences of the human test subjects.

Harman reported their results at r = .86 with p < .05.

I expect that some test fixtures may perform better than others.

Thanks DT

Hello.

Thank you, I have reread and digested the Harman papers and Hearing-aid international standards. Much or most of this is focused on the function of the human ear and the SLP at the ear drum, or the DRP. You seem not to give credit for knowing that. As it turns we are using hearing aid technology to measure headphones.

To develop the Harman target curve, Harman put headphones on many test subject heads. The test DRP was the test subjects very own ear drums. This is a psychophysics scaling technique not an actual measurement of the SPL. The specific, if it was measured, SPL at the test subject DRP is unimportant as long as the test subject’s response is consistent over multiple test iterations.

Now you have a box of test headphones, recorded sound test tracks and human preference data.

If we were starting from scratch we could use our box of test headphones, recorded sound test tracks and human preference data to develop a target curve for the current GRAS 45 CA-10, the HATS 5128 or some other test fixture. We could even use the older version JBL Modified GRAS 45 test fixture to develop a target curve. Each curve is specific to its own test fixture.

The goal is to develop a target curve that will accurately reflect the preferences of the human test subjects.

Harman reported their results at r = .86 with p < .05.

I expect that some test fixtures may perform better than others.

Thanks DT

Those are all good points.

<<<If we were starting from scratch we could use our box of test headphones, recorded sound test tracks and human preference data to develop a target curve for the current GRAS 45 CA-10, the HATS 5128 or some other test fixture. We could even use the older version JBL Modified GRAS 45 test fixture to develop a target curve. Each curve is specific to its own test fixture>>

How is that different from the paper I presented at the HBK Seminar? I essentially took measurements of headphones that had been evaluated subjectively and measured on the GRAS45CA MOD (which you call JBL Modified) and measured the same headphones on a B&K 5128 to derive a target curve for that fixture. What would you do differently?

 

[ADU]

Harman's preferred in-room curve is the red curve on the left in this diagram

Corrected.

Have you seen Chris Struck's paper on deriving in-room eardrum response from HRTFs, room acoustic parameters, and speaker directivity? I made a spreadsheet including the Harman room data at one point, I believe @Robbo99999 has it still.

Nope. I haven't. But thank you for the above link, Mad_Economist. I have tried to read as many of the white papers on this subject as I can, including some of the papers published by Harman, or covered in their various video presentations to different audio groups. But I'm not an AES member. So I don't have access to all of that content.

I believe that Theile's position as of 2016 is that the DF target with preferential adjustments matching your adjustments to the in-room baseline of the Harman studies would be preferable for normal stereo content - that is, that the Harman target is correct

I don't know this fellow either. If he's sayin that the compensated diffuse field response of a headphone should be close to the tilted diffuse sound power response of a good loudspeaker in a room though, then I'd agree. That is really all this boils down to imo.

The disagreements and arguments about how well-extended that upward tilt should be in the lower frequencies are good to have. Because not everyone is mastering their content on equipment that is as well extended into the sub-bass frequencies as some of the examples that I posted above (even though that can be accomplished fairly easily with the addition of a sub-woofer in most cases)... Nor should they in some cases, because sound mastering probably always depends to some degree on your target listening audience, and whatever their playback equipment preferences are. Most of the better headphones that are well-extended in the bass and that track the Harman curve in that area seem to follow this general model though.

10 headphones that are well extended in the bass, with diffuse field compensation...

Headphones included in the above diffuse field plot include the AKG K371, Apple APM, Audeze Sine (with Cipher cable), Beyerdynamic Custom One Pro Plus (velour pads & bass setting 3), Neumann NDH-20, Onkyo A800, Philips Fidelio X2HR, PSB M4U 8 (with ANC on), Sennheiser HD598CS and Sony MDR-7506. The headphones that are rolling off a bit more in the sub-bass are mostly open-back models. And the headphone that dips down significantly in the upper mids is the Neumann. And the one with the dual peaks in the low treble is the Sony MDR-7506.

The same group of headphones with the average sound power response of the five best extended loudspeakers in my previous post overlaid in black...

Same group of headphones with the average sound power response of the three best extended speakers in my previous post (namely the Dutch & Dutch 8C, KEF Reference 5 and Infinity Intermezzo 4.1t) overlaid in black...

I would not recommend using the above sound power curves as targets for a neutral headphone's response in the treble though with Ora's DF plots. Even though they seem to be tracking the average responses of the headphones' peaks (which is what I generally look at) in that range as well.

You can certainly try it, if you want. Imo though, some adjustments are needed to better approximate a neutral response in the treble and upper mids on Oratory's diffuse field graphs, perhaps more along the lines of what's shown here, to perhaps compensate for some effects of the pinnae he's using. And maybe some other differences between his gear and the specific configuration of hardware that GRAS may have used to calculate their DF compensation curve. And to also take into account some of the directivity/cross-overs errors which are fairly common on other speakers (like this one) at around 2 kHz in the upper midrange frequencies.