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 came across my desk only 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 they 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 which 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 results of all that effort were 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 they’re 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 whether 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.
    Brent Butterworth · 7 months ago
    @Siana It's absolutely possible to do that. It's called measuring in phons, which is a unit of loudness that corresponds to human perception rather than to a fixed 0 dB reference at all frequencies. The listener compares two adjacent frequencies and adjusts them to be the same, and after going through a lot more frequencies, ends up with a target response that matches that listener's equal-loudness curve (and probably comes close to most listeners' loudness curve).

    Bob Carver told me he voiced his Sunfire ribbon speakers this way, and that he got the idea from BMW, whom he consulted with on car audio systems. But it takes a long time, and TMK, there's no research that proves its efficacy in creating superior products.
  • This commment is unpublished.
    Siana · 7 months ago
    @Bernd Hey you appear knowledgeable, so sorry for barging in, but i have a challenge for you. It's about something you said - the lack of test setup that would measure what you actually hear. Do you think it's possible to fix that? Do you think it's possible to devise a series of listening challenges with synthesized noise or test audio of some kind, where the listener would be presented with two of these at a time, and be prompted to decide which one is louder, or turn a knob until they appear identically loud, and from a series of such results, build a frequency response of a particular reproduction device, be it speakers or headphones, from the perspective of a given listener?

    As to my credentials and affiliations, as this tends to come up in this thread - none, and my motivation is mere curiosity. I do not have any formal education related to audio, i have not done any hands-on research, and i do not work for any audio company or the like and never did, and while i immensely enjoy music, i'm probably not what audiophiles would recognise as one of them - my preferred headphones are Yoga CD68 that i got for 20€, hanging off the 10€ genuine Apple iPad USB-C to headset adapter plugged into a dumpster-dive PC, and i don't have any access to expensive stuff and never did. But maybe with some guidance i could get something going, and i'm strongly inclined to make it free and open-source, to make it potentially maximally useful to researchers, and easily accessible to the general public.

    As to how good and applicable the Harman curve is? I don't know, but "let's copy Beats Solo V1" curve probably isn't terribly hard to beat.
  • This commment is unpublished.
    andy · 1 years ago
    @Todd H.
    there is enjoy
  • This commment is unpublished.
    Brent Butterworth · 1 years ago
    @Todd H. That would be challenging, since even Harman isn't forthcoming about which of its models use Harman curve. But for about a year we've been including a comparison with a known Harman curve headphone in the measurements, and now that we have some headphones that are pretty much right on the curve, that'll be a more useful comparison.
  • This commment is unpublished.
    Todd H. · 1 years ago
    I wonder if someone will compile a list of headphones with the Harman Curve. I don't think Harman will. Maybe you guys?
  • This commment is unpublished.
    Mauro · 1 years 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! (mm)
  • This commment is unpublished.
    Mauro · 1 years ago
    @Brent Butterworth 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.
    Brent Butterworth · 1 years ago
    @Dustin Apparently. I wish JBL and AKG would market this, and show the Harman curve and the headphone's measurement on the web page for each model. Why does it have to be so complicated to find out how these things are voiced? Having worked in marketing, I know that there's always somebody who says, "Oh, we can't do that because blah blah blah ..." but in this case there's just no downside at all.
  • This commment is unpublished.
    Brent Butterworth · 1 years ago
    @Mauro 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.
  • This commment is unpublished.
    Mauro · 1 years ago
    @Dush 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.
    Dush · 1 years 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.
    Brent Butterworth · 1 years ago
    @Dustin 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.
    Atle · 1 years ago
    @Bernd 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.
    Solo Administrator · 1 years ago
    @Bernd 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 · 1 years ago
    @Brent Butterworth 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 · 1 years ago
    @Mauro I'm going to try to find a pair in a store or something and give them a listen.
  • This commment is unpublished.
    Brent Butterworth · 1 years ago
    @Bernd 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.
    Bernd · 1 years ago
    @Brent Butterworth 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.
    Mauro · 1 years ago
    @Mauro 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!

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