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It’s hard for me to believe it’s been seven years since researchers from Harman International presented the landmark paper “The Relationship between Perception and Measurement of Headphone Sound Quality” at the 2012 Audio Engineering Society Convention in San Francisco -- the first paper in which the company presented what became known as the “Harman curve,” the target frequency response that average listeners would like best. When I first read that paper, I assumed it would quickly revolutionize the headphone business. As a headphone reviewer, I knew that the various headphones and earphones then on the market often exhibited wildly different sounds -- even among different models in a company’s line -- which indicated that knowledge was lacking or simply being ignored.

Sean Olive

Yet we didn’t see a surge in headphones claiming to use the Harman curve -- not even from Harman companies AKG, JBL, and Harman Kardon, although other manufacturers had quietly confided to me that they were basing their designs on the Harman curve. In fact, the first set of passive headphones I’ve received from a Harman company using the Harman curve only came across my desk last month: the AKG K371s -- and the only way I knew that they were voiced within 1dB of the Harman curve was by reading a Facebook post from Harman senior fellow Sean Olive.

It looks, though, like the dam is finally bursting. In a presentation last month to the Los Angeles chapter of the AES, Olive highlighted several other headphones and earphones designed along the lines of the Harman curve (although not, as best I can tell, marketed as such). The earphones include Samsung Galaxy Buds; JBL Live 200s, Live 500s, Live 650s, and Reflect Flows; and AKG N5005s. Headphones, for now, seem to include only the AKG N700 NCs, K371s and K361s, but we can expect more. As Olive told me later in an e-mail, “Basically all new AKG headphones are designed to Harman target and for the past year JBL has followed it but with 2dB extra bass below 125Hz.”

Olive’s presentation detailed Harman’s ambitious research into headphones, which has since 2012 resulted in 19 papers, one patent (and three more pending), and a one-click routine for the SoundCheck audio measurement suite that uses the Harman curve to predict listener preference. The effort started with the realization that, as Olive put it, “There were standards for diffuse-field and free-field headphone response, but no one was following them so there must have been something wrong.

201911 akg twist

“At the time, our marketing department was telling us that we should duplicate the response of Beats headphones, because those were the best-sellers,” he continued. But Harman’s researchers had already evaluated those headphones in blind tests, and found them to be unpopular among their listeners. “So we told them they should duplicate Beats’ marketing instead,” he said.

The researchers’ idea was that if headphone designers knew what measured response best suited the largest number of listeners, the designers could then tailor their products’ frequency responses to that target. This would be more efficient than “shooting in the dark” by building headphones, putting them through listening tests (which, if you want them to be blind, are much more complicated with headphones than they are with speakers), then repeating the process until most of the listeners are pleased.

Harman’s first effort involved a blind test of six over-ear headphones, followed by measurements of those response curves to see what response pleased the most listeners. Subsequent projects solicited the judgment of hundreds of listeners around the world, and measurements of hundreds of different headphones.

Sean Olive

The result of all that effort was Harman curves for earphones and over-ear headphones. But as Olive suggested in his above comment about JBL headphones, it’s not a “one-size-fits-all” target. His presentation identified three potential groups to which manufacturers can target their headphones.

“Harman curve Lovers”: This group, which constitutes 64% of listeners, includes mostly a broad spectrum of people, although generally under age 50. They prefer headphones tuned close to the Harman curve.

“More Bass Is Better”: This next group, which makes up 15% of listeners, prefers headphones with 3 to 6dB more bass than Harman curve below 300Hz, and 1dB more output above 1kHz. This group is predominantly male and younger -- the listeners JBL is targeting with its headphones.

“Less Bass Is Better”: This group, 21% of listeners, prefers 2 to 3dB less bass than the Harman curve and 1dB more output above 1kHz. This group is disproportionately female and older than 50.

According to Olive, his group still has some more research into headphones to do, but they’re starting to wrap it up and anticipate moving on to new projects. We don’t yet have enough information to know if the Harman curve will result in greater sales, millions more happy listeners, and better standardization of headphone evaluation. I’ve learned from listening to several headphones and earphones that come close to the Harman curve that it is, at the very least, an excellent baseline for performance. Headphones and earphones may, for various reasons, deviate to some extent from the Harman curve. But if their measured response is far from the Harman targets, listeners and reviewers should at least question why, and the manufacturer should be able to respond with a plausible rationale based on research and testing.

I expect we’ll encounter manufacturers and reviewers who simply claim, “I listened to some Harman curve headphones and I don’t think they sound very good.” Audio enthusiasts will then have to decide if they trust the conclusion of a single person, determined through casual, sighted testing, or the conclusion of years’ worth of research conducted with hundreds of listeners in carefully controlled blind tests. I know which way I’ll go.

. . . Brent Butterworth
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  • This commment is unpublished.
    Mauro · 13 hours ago
    I would like to share an alternative to equalize headphones, which is entertaining and helps training critical listening skills...

    Check out this software from Harman that they use to train their listeners: http://harmanhowtolisten.blogspot.com/2011/01/welcome-to-how-to-listen.html.

    After some experimentation with it (and the now-gone Philips Golden Ears website), I used to play pink noise to equalize my headphones. In fact, pink noise is pretty helpful to detect bright spots or more elevated areas in the frequency response.

    In the end, I happened to like my equalization curves... I hope you'll do the same!
  • This commment is unpublished.
    Dush · 7 days ago
    In an age of EQ the differences between headphone sound aren't the primary driver for my purchase anymore. Things like comfort, features and ANC are far more important. I can then get the headphone sounding however I want via EQ. Check out the AutoEQ project for thousands of headphones that are EQ'd to the harman target curve.
    • This commment is unpublished.
      Mauro · 7 days ago
      Thanks Dush for sharing!
      I will give it a try for sure!!

      do you have a suggestion for an equalizing app for PC and smartphone? I remember Tyll using DMG Equilibrium on PC..

      There is a nice article On Medium by the project author called “Equalizing Headphones the Easy Way”

      I have to admit that after having tested eq room compensation for speakers, I ended up being a bit skeptical on applying high and wide-range compensations. They usually add more harm than good. Never understood why exactly but maybe Brent Butterworth can enlighten us! Maybe time group delays?? Dunno!

      in the meanwhile my Audyssey speaker eq settings are limited to less than 500hz just where it is needed for room modes compensation. But I have to say that my speakers are quite close to neutral so it not needed above that and I would love to apply the same approach with headphones to avoid artifacts introduced by eq.

      anyway an headphone sound quality is not just about Frequency response. Frequency response does not tell you a lot about distortion, group delays and decay.. I guess that’s why active designs are not usually among the best? Brent Butterworth what is your experience with active headphones with dsp?
      • This commment is unpublished.
        Brent Butterworth · 6 days ago
        Active designs have the potential to deliver the best sound, but of course an EQed active design is only as good as its target curve -- as you found with room EQ built into A/V receivers. I think the only headphones with auto EQ that I've tried were a JBL set, and the results were just OK, probably because what they really need to EQ for your ears is an insert microphone in your ear canal. I'm hoping that the photo-based auto headphone EQ systems will be developed to where they're reliable. https://www.soundstagesolo.com/index.php/features/209-2019s-most-important-headphone-presentation
        • This commment is unpublished.
          Mauro · 6 days ago
          I will check it out!

          in the meanwhile I have checked out the AutoEQ project and tried to compensate with the software Equalizer APO a very bassy headphone Logitech UE6000.
          The result was terribly harsh.

          this made me think of the nice article of Tyll explaining THD measurements and how much distortion, modal break ups and resonances of a compromised design such an headphone can contribute to affect sound quality!

          I guess it is not so trivial compensating headphones. Some quirks hidden by the designer might be exposed!

          Brent Butterworth About your THD measurements. Do you find that there are correlations with critical aspects of the headphone you are measuring as Tyll thought?
  • This commment is unpublished.
    Bernd · 10 days ago
    Brent, you should mention the listener base used in Olive's studies. For someone with an academic background in studies on subjective evaluations (which are notoriously hard to nail down), neither the number nor the diversity and balance of subjects is satisfactory. (Of course, Sean knows this very well, but his aim is just to do corporate research directly linked to product development).

    We are talking about taste here. Check out the diversity of restaurants in any bigger city. More or less the same goes for taste in music, sound quality, voicing, equalizing, spatialization, ... , which all depend on age, gender, cultural background, social factors, music genre, listening situation and time of day, with/without video, and other factors.

    This serves to illustrate that the pure notion of having 3 variations of 1 curve, which are supposed to serve all of the above, is not meaningful at all. There is sufficient justification to have not only various wearing styles, colors, comfort features, connectivities, but also voicings. Even McDonalds has much more than 3 items on their menu, and Subway offers quite some variation in seasoning, vegetables, sauces etc., even though some distinguished star cook will insist there is only one "perfect" preparation for chicken fillet and one perfect wine to be served with it.

    When conducting a really scientifically solid study with the required thousands of listeners needed for good statistical significance, which also accuratly represent the demographics of interest, I would expect to find a complex, wide landscape of preferred target curves. If you're lucky, that landscape can be partially parametrized and linked to demographic or other factors of the listeners, perhaps. Other than that, maybe some rather vague features will surface which describe generally favourable or unfavourable curves. Manufacturers might then aim at avoiding the unfavourable features, but if they don't, then those products should fail commercially - or not, which would prove that a sufficient amount of users cares less for sound quality than for other properties of a headphone.
    • This commment is unpublished.
      Atle · 8 days ago
      Is there difference between accurate colour on TVs? Is it meaningless to have a accurate colour reproduction on a TV, since people are different? Meningless to have a good black leve, people are different? The job of the hardware is to reproduce in the best way possible, that is not very individual, the variation comes in the music.
    • This commment is unpublished.
      Brent Butterworth · 10 days ago
      The listener base for "A Statistical Model That Predicts Listeners' Preference Ratings of In-Ear Headphones" was 71 listeners, ages 20 to 59, and 82% male, roughly half trained and half untrained listeners. In "Factors That Influence Listeners' Preferred Bass and Treble Levels in Headphones," they used 249 listeners, with groups in Michigan, California, Germany and China, ages 18 to 70, 89% male. Sean admits that he'd like to have more female listeners, but as someone who's assembled listening panels for 25+ years, I know how challenging it is to recruit female listeners for audio tests.

      Can you present evidence that a scientifically solid audio study requires thousands of listeners? That claim would invalidate most listening-based research. Can you present evidence that a wide variety of listening curves is needed? That contradicts the results of the Harman studies, and TMK there are no competing studies that have disproved their contentions.

      It's common in audio for people to dismiss measurements, listening tests, etc. as invalid because they find some flaw or inconsistency, real or perceived. But the alternative, especially in high-end audio, is not studies with more listeners or a different methodology. It's one guy, often with spotty knowledge of audio research, a tenuous (or non-existent) connection to music performance and production, a set of ears with many decades of wear and tear on them, and sometimes without even a solid grasp of engineering, declaring that he knows what music is supposed to sound like and he's created a product that "sounds like music" or some other vague claim that can't be proven or disproven. Then a reviewer, who likely also fits the above description, and who uses no evaluation process deserving of the term "method," provides flowery verbiage to support the claims.

      There are high-end designers who really do know the research and engineering, and who create terrific products (Paul Barton, Andrew Jones and Laurence Dickie all come right to mind, but of course there are many, many others), but the gut-feel "process" I describe above is probably at least as common. This is exactly the kind of thing that scientific research is intended to combat, and for which I personally have no respect.

      My attitude is, if you want to criticize scientific research, cite references to back up your claims, and invest the time and resources to find a better answer.
      • This commment is unpublished.
        Bernd · 10 days ago
        Thanks for you reply, Brent. Actually I've conducted and partially published a fair share of listening tests myself, at university and later in product development, so I'm speaking from experience as well.

        But I believe we both agree on the difficulties when trying to achieve reliable, repeatable, and valid listening tests and comparisons. They are impaired by short acoustic memory, choice of stimuli, listener fatigue, conflict between isolation of factors vs. interdependence of factors (esp. with headphones: wearing comfort, sealing, usage of EQs or presets, heavy pre-processing/sweetening by streaming services, listening situation and intention, ...); sometimes a fully double-blind design just isn't feasible; etc.

        And since most headphones are targeted at the worldwide market, then this worldwide population should be correctly represented in the study; the same goes for the various listening scenarios, target groups (defined by more than age, gender and nationality) etc. for which the products are designed and marketed.

        Next is the difficulty of measuring what you actually hear; standardized pinnae and couplers only enable repeatability, but don't necessarily replicate what arrives at your ear drum. Sometimes, narrow details in the response are just as important as the general FR envelope, but can't be represented in "cookbook recipe" curves. In all this, we aren't even talking about driver type and size, transient behaviour, linearity etc. yet, which also influence preference.

        When considering all this, as well as all the factors I mentioned in my first post, it should become clear that we are dealing with a really really complex problem, if we aim at fully "solving" the question of how a headphone should sound. Achieving validity (representativeness and meaningful methods) as well as reliability (significance and repeatability) despite this complexity, is what leads me to the admittedly vague estimation of "thousands" of listeners. I didn't say that every listening test has to be very large, but if you strive for universal answers regarding headphones, that's what would be needed. And yes, often the standard deviation or confidence of listening test results doesn't improve when increasing the number of repetitions or listeners, which then indicates that the test design is flawed or that the subject matter is very difficult to determine.

        So don't get me wrong, I'm all for the scientific method, we don't need to debate here about the details of how to apply it to preference testing. I'm just saying that practicable studies are always very limited, given the vast overall complexity of the subject, and therefore the range of valid conclusions is very limited as well. Treating Sean's results as universally valid would be disregarding those limits of validity.

        My ultimate point is that we shouldn't demand all new headphones to converge towards the Harman curve - there are many good reasons (some of them mentioned before) for implementing a different voicing. Seeking *the* one (or very few) "holy grail" curves seems somewhat similar to the gut-felt "this is the ultimate"-claims of the high-end gurus which you understandably say you have no respect for.
        • This commment is unpublished.
          Brent Butterworth · 9 days ago
          Unfortunately your anonymity prevents me from confirming your research work; I hope you'll be willing to share your identity, and I think it's appropriate, necessary and courteous to do so when you're criticizing another researcher's work.

          I've not stated or implied that the Harman Curve is the "holy grail," and neither has anyone from Harman, to my knowledge. As I've stated in reviews, I haven't necessarily found that Harman Curve headphones sound best, but they all sound good, to me and the other listeners I work with. That's why I said it's a useful baseline.

          And in my opinion, that's what we want: a headphone that sounds good. While it's common to suppose that listeners have radically different tastes, and would thus need all sorts of different headphones, I don't know of any research that confirms this supposition, and I do know of research that refutes it. In fact, Harman did exactly this research, and found that with 238 test subjects in three countries, preferences were generally consistent, “regardless of the listeners’ experience, age, gender and culture.” Saying that "practicable studies are always limited" is not a substantive refutation of this or any other research.

          While I'm guessing this is not your intent, what you're saying reminds me of what I hear from many high-end audio writers and audiophiles. To wit: Science is so complicated and uncertain that we can't really know anything for sure, so in the absence of absolute certainty, I'll just believe whatever feels right to me. Or as my friend Dennis Burger once summed up this view, "Science is sometimes wrong, so homeopathy works."

          And then what do we have to judge audio products by? Totally subjective reviews from people who mostly fit the description in my previous post. I'll pass. We have good science here and I intend to use it and promote it.

          It doesn't sound to me like you're intentionally advocating the "faith-based" approach to audio that most high-end publications take, but as I see it, the end result is the same -- unless you can present something better than the existing research. And I certainly encourage you to do so, and I promise to write about it if you do!
          • This commment is unpublished.
            Bernd · 9 days ago
            Again, I think we are largely in agreement. I'm sorry if it still seems I am unjustly criticizing Seans's research, that's not my intention, it is very well done within the limits it had to deal with, and which are properly declared.

            And yet, the temptation is quite great to just ignore those limitations and run with the target curve, applying it to all kinds of products, use scenarios and demographics without reflecting on the validity and applicability (especially higher management is good at that, giving the experts a hard time). Neither you nor Sean are doing that explicitly, still the mere existence of a seemingly simple recipe can in many cases do more harm than good. That would be my only issue with Sean's work.

            Of course, the term "holy grail" is deliberate hyperbole on my part, you obviously didn't write that. But the message of your blog entry seems to be that the Harman curve is pretty good and anyone not aspiring to it should better present good reasons - which in my opinion is not a meaningful demand, for the many reasons already outlined.

            If I were to write here in my current professional function, I wouldn't be able to discuss these matters openly, hope you understand.
            • This commment is unpublished.
              Brent Butterworth · 9 days ago
              I appreciate the reluctance to present a target curve of any sort. We have actually been discussing this for a couple of years at SoundStage -- whether or not to present or refer to the Harman curve as a reference in reviews. Now that the research is basically done, and there are lots of examples out on the market, I think it at least gives us a point of comparison -- just as the NRC guidelines have done for speakers for about two decades now.

              And if someone deviates from that, they're free to make their case. For example, I expect HiFiMan's not going to run with it for the most part because Fang Bian has told me his customers like extra treble. That's fine, and I keep that in mind when I review those headphones. In fact, I'll bet we'll find companies selling against the Harman Curve, proclaiming that Harman is a big corporation and they don't understand music, or something like that.
              • This commment is unpublished.
                Dustin · 9 days ago
                It seems to me that the science done by Sean Olive is the best source of information we have on what makes a headphone sound good. Sean Olive and his team and doing for headphones what Floyd Toole did for loudspeakers. Of course there might be limitations based on limited study. But the more study that occurs the more we can narrow in on the truth. It seems to me that him and his team have done enough research to reasonably suspect that they are on the right track.

                Using a parametric equalizer and a MiniDSP EARS, I have personally tried to EQ all of my headphones as close as possible to the Harman Target (within the limitations of my measurement gear, of course), and I feel it has improved the sound of every single one. I don't understand why more manufacturers don't seem to follow what this science suggests. But I do suspect we will see things trend in that direction.

                It's also shocking how little correlation there seems to be between price and performance. Yet, we still have legions of people over over the internet (thinking: Head-Fi) that stick to the belief that more expensive headphones must sound better.

                I believe this science is an absolutely huge step forward in the right direction in an industry that is filled with dogma, misinformation, and outright lies.

                Given the difficulty in doing one's own measurements, I only wish there were better ways to determine which headphones come closest to this target. I know there are a lot of different websites now that do conduct their own measurements, but they are not all equal and the measurements are not always consistent among sites. I think the closest we had was Tyll at Innerfidelity, but sadly that website has devolved now into nothing more than a marketing tool. They don't even allow comments on their website anymore. I can only imagine how Tyll must feel about what's happened.

                I think this site is now the nest best thing. And, Brent, I suspect your measurements might be even more accurate than Tyll's. I personally think it would be excellent if you could super-impose the Harman Target onto your headphone measurements. After all, it can be tricky interpreting the measurements as you display them (in their raw format, I mean).
                • This commment is unpublished.
                  Brent Butterworth · 8 days ago
                  Thanks! That means a lot, especially comparing me with Tyll. I would say Tyll's measurements and mine are similarly accurate -- both done with pro-level gear and reasonable practices -- just somewhat different. I basically copied what I could from him, and discarded what didn't work so well for me or that I thought was not super-clear to me in terms of its benefit.

                  My analyzer won't let me show an externally generated curve, but I can show a measurement of a Harman Curve headphone or earphone on the comparison chart. I usually do that now, and intend to do it more in the future now that there are more models coming out.

                  The one thing I wonder about is how well it applies to open-back models. Open-back models don't have that big bass hump below 125 Hz, yet many sound fantastic, and balanced. I should do some listening tests and measurements to try to figure that out.
    • This commment is unpublished.
      Bernd · 10 days ago
      (the comment function replaces the number three with hearts, for some reason, testing again: 3
      • This commment is unpublished.
        Solo Administrator · 9 days ago
        You are correct that the 3 was generating a heart graphic. It was an emoji set up in the system -- but has been eliminated so 3s will show up correctly now.
  • This commment is unpublished.
    Dustin · 11 days ago
    Very interesting. Do you know which JBL headphones have been voiced to the harman target with the added bass?
  • This commment is unpublished.
    Mauro · 11 days ago
    I’d like to add that my perception reading reviews and measurements is that gaming headphones have more easily accepted the Harman curve as can be seen on Rtings for example.
    Have you tried any?
    in these days I bought a few open headphones to try myself and the first one, Sennheiser PC373/game one (tweaked version of 598), seems to be quite close to my NAD HP50. Very nice headphones at around 100€!
    • This commment is unpublished.
      Brent Butterworth · 11 days ago
      I haven't tried any gaming headphones -- too scared to go down another rabbit hole!
      • This commment is unpublished.
        Brent Butterworth · 9 days ago
        But I really should, huh? I'll look into it ...
        • This commment is unpublished.
          Mauro · 9 days ago
          Eheh, I didn't want to put the bug in your ear!

          It's something I have been wondering about as well.
          I guess that being the target audience pretty young they have competitive prices and frequency response is good also because they are usually active designs..so worth considering for the budget-minded fascia.

          About the specific headphone, I would say that from 60 Hz to 7kHz is pretty spot-on. Below 60Hz drops quickly, but I guess it might be expected given the dimension of the driver, right?
          At around 8Khz there is a little hint of "sss" sound, that make voices a bit lipsy, but not a big deal honestly.

          My quest into open headphone is moving to Philips Fidelio X2 I found at around 100€, very entertaining! They have a huge soundstage! A pity some bloat at very low frequences and a quite predominant "sss" sound at top, that makes treble a bit artificial..

          Waiting to get the LCD-1 I have just ordered on your suggestion!
          • This commment is unpublished.
            Mauro · 9 days ago
            I was forgetting for those interested, no bass bump below 200Hz for the Sennheiser PC373/Game One makes bassy instruments recessed, as if they were further away on the stage. And in my experience playing with subwoofers, bass seems to contribute quite a bit in enlarging the soundstage, which in this case remains good, but not great!
  • This commment is unpublished.
    Mauro · 11 days ago
    Interesting! I remember Paul Barton saying that above 8khz measuring instruments could not give adequate measurements and he was experimenting with molds of ear canal cadavers!! Creepy..Harman is confident also on high treble?
    • This commment is unpublished.
      Brent Butterworth · 11 days ago
      No, Sean said the curve is valid only up to 8 kHz. The new "high-res" ear simulators can now do consistent measurements up to 20 kHz or so, but given than the response of human ear canals above 8 kHz varies so much, we don't yet know what >8 kHz measurements really mean.

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