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 · 6 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 · 6 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 · 11 months 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.

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