Researchers at Harman International tried to find the ultimate headphone sound signature, so they came up with the Harman curve.
What is Harman Curve?
The Harman Curve is the optimal sound signature that most people prefer in their headphones, as discovered by Harman International. It’s a close representation of how quality speakers sound in an ideal room. It shows the target frequency response of perfectly sounding headphones, what levels should be boosted, and which subdued (graph below).
That’s why the Harman curve (also “Harman target”) is one of the best frequency response standards for enjoying music with headphones.
Compared to the flat response, the Harman curve has slightly elevated bass and treble (a few dB on each side, see the graph below).
When Was the Harman Curve Created?
The “curve” was created in 2012 by a team of scientists, with audio engineer Sean Olive overseeing the project. It was published in “The Relationships Between Perception and Measurement of Headphone Sound Quality” paper.
The research involved extensive blind testing on various individuals trying out different headphones.
Based on what they liked and disliked, researchers found and defined the most universally liked sound signature.
They tested both for in-ears and over-ear headphones since both require different tuning to provide similar results.
Why was Harman Curve Created?
Harman had a mission to create a target frequency response measurement, which perfectly represents how quality speakers sound in an ideal room.
Even after extensive research of the past decades, audio engineers only knew how to tune speakers to sound flat.
However, when it comes to headphones, every company tuned their products based on what they thought sounded good.
Tuning headphones can be problematic due to human anatomy. Everybody has a slightly different pinna and ear canal, affecting how each induvidual perceives specific frequencies. In extreme cases, there is a couple of dB difference from person to person.
Also, sound, if not absorbed, reflects from other surfaces. Therefore, even your torso can make you hear music differently than your friend.
Headphones only interact with the pinna and ear canal, while earbuds skip the pinna entirely and go straight into the canal.
Therefore, tuning that is perfect for speakers isn’t ideal for headphones.
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How Was Harman Curve Created?
Sean Olive and his researchers said that both free and diffuse fields aren’t perfect for tuning headphones.
The reason is that none of them was created in a realistic listening environment. Sean proposed:
- To place good speakers in a regular listening room. It shouldn’t be too reverberant nor too anechoic.
- The room had around 0.4 seconds of reverberation time, close to 0.3 seconds of professional studios.
- The artificial head later measured frequency response, which listeners immediately liked. The resulting curve is Harman curve.
Reverberation is an effect when the sound from one source starts bouncing from other surfaces. That makes that sound appear bigger, while the room can add “flavor” to it (boosts specific harmonic frequencies), making it more dry or warm.
An anechoic chamber is a well-treated room where there are no echoes. All the sounds get easily absorbed in materials such as foam pyramids. These rooms are excellent for testing the loudness of various equipment, from speakers, home appliances to car engines.
Why speakers sound different than headphones in a room?
In a normal room, like the one used in the research, there is reverberation. The latter plays a crucial role in shaping the sound we later hear.
In this case, a normal room slightly boosts up the bass since low frequencies are the hardest to absorb.
In contrast, high frequencies get easily absorbed, so we need to compensate slightly for the loss.
That is also how sound engineers in studios hear the music when mixing, which is why Harman curve is the closest response to the “original” sound of the recording.
How Many Harman Curves are There?
After almost a decade, we got 4 different iterations of the Harman curve. Each of them shows slight changes in what people prefer to hear.
In the last iteration from the year 2019, the curve received a slight boost in bass and smoother treble.
What Headphones Use Harman Curve?
Officially, not many. However, if you look at the best ones, almost all have very similar frequency responses to the Harman curve.
Of course, even Harman uses different variations of the target curve on their headphones. The reason is that every person hears differently, so there is no universal headphone sound to please them all. The latter was also apparent in testing.
- Around 64% of listeners, even those working in the audio field, enjoyed the Harman curve the most. Almost all Harman curve lovers were younger than 50.
- 15% of listeners preferred more bass. In practice, up to 6dB elevation below 300Hz, and 1dB boost above 1kHz. This group consisted of younger males, which is also a target audience for JBL headphones.
- The remaining 21% of users, enjoyed less bass. The low-end was reduced up to 3dB, while the 1dB boost above 1kHz stayed the same. In this group, you find primarily females and older listeners.
Should You Buy Headphones with Harman Tuning?
As of right now, the Harman curve is the best approximation of how the studio recording should sound like. So, if you want to experience the music as intended, we recommend checking Harman-tuned headphones. The AKG K371 and K361 are the most well-known.
Of course, you have to take into consideration that all humans hear differently. That means some might not like the sound of the Harman curve.
As always, if you have the option, listen to headphones with the Harman headphone curve before buying.
What Other Headphone Response Curves Exist?
Usually, engineers used free-field or diffuse-field tunings.
It was created by measuring a flat speaker in an anechoic chamber. The latter is made so that the sound gets easily absorbed in the walls.
A human dolly was placed at the precise spot in the room, right in front of the speaker. Microphones inside dolly’s ears later measured the sound.
The problem was that nobody lives in an anechoic room, which makes for an unnaturally perfect sound. That’s why the Free-field curve isn’t very popular.
Diffuse field response
This response takes a different approach by using a very reverberant room. Instead of one speaker, there are many of them placed around the dolly. All of them measure flat.
The idea was that since the sound bounces from all surfaces, we tend to hear it from all directions. That also makes it more “natural.”
Practically, the diffuse field curve is near flat but with a brighter treble.
The most well-known headphones that use the diffuse field curve are Beyerdynamic DT 880 Pro, AKG 240DF, and Etymotic Research ER4 Series.
Frequently Asked Questions (FAQ)
Is The Harman Curve Flat?
Harman curve sound signature is a close proximation of flat speakers in a studio environment. Due to room reverberation, it technically doesn’t sound neutral, but it’s still a close representation of what an original recording should sound like.
What is Neutral Sound?
As the name suggests, neutral (or flat frequency response) means there are no boosted frequency ranges. The whole frequency spectrum is equally represented. That kind of sound signature is essential for mixing and mastering in studios.
However, a purely neutral response can sound quite dull, so people like to spice things up by boosting bass or treble.
How Do You EQ Your Headphones?
All operating systems already have built-in equalizers to tweak the sound quality of your headphones.
You can also help yourself with downloadable software/apps, some of which are free, while others are locked behind a paywall.
The best ones are Equalizer APO, FxSound, Boom 3D, and Bongiovi DPS.
Check our guide on how to boost the bass on a computer.
Does Harman owns JBL?
Yes, Harman International (previously called Jervis Corporation) bought audio company JBL in 1969.
Harman also owns Harman Kardon, AKG, Bang & Olufsen automotive, Lexicon, Soundcraft, and many others. Harman was later sold to Samsung in 2017.