What is Harman Curve (DEEP Research)

What is Harman Curve Technology?

What is Harman Curve?

Harman International has discovered the Harman Curve, which is the best sound signature for headphones. It is an accurate representation of how high-quality speakers sound in ideal rooms. It illustrates the target frequency response for perfectly sounding headphones. It also shows how to adjust the volume and what levels to increase.

This is why the Harman curve (also known as Harman target) is one the best frequency response standards to enjoy music with headphones. Contrary to the flat response, Harman curve has a slightly higher bass and treble than the flat one.

Harman International is Harman’s historical name. Harman International was established in 1953 as Harman Kardon. Harman International grew over the decades with a number of acquisitions and expansions. It has become a global audio technology leader and a leader in psychoacoustic studies.

When was the Harman Curve first created?

The “curve”, which was developed by a group of scientists in 2012, was overseen by Sean Olive, an audio engineer. It was published by “The Relationships Between Perception and Measurement of Headphone Sound Quality” paper.

Research involved blind testing various headphones against various subjects. The most liked sound signature was determined by the researchers based on their opinions. Because they require different tunings, both in-ear and above-ear headphones produced similar results.

Harman Curve is a widely-used term that reflects this newfound knowledge about headphone response curves. The Harman Curve essentially refers to a frequency response that produces the “best sound” for headphones.

Why was Harman Curve created?

Harman was on a mission to develop a target frequency response measurement. This perfectly represents the sound quality of high-quality speakers in an ideal space. Audio engineers were still unable to tune speakers to sound flat, despite extensive research over the decades. Headphones are the same. Every company has their own preferences.

Due to the human anatomy, tuning headphones can prove difficult. Every person has a slightly different pinna or ear canal. This can impact how each individual perceives certain frequencies. Extreme cases can lead to a difference of up to 2 dB between individuals. Sound can also reflect from other surfaces if it isn’t absorbed. Even your torso can affect how you hear music.

While headphones only interact with the pinna or ear canal, earbuds go directly into the canal. So, headphones are not the best choice for tuning speakers.

How was Harman Curve created?

Harman chose to experiment with the Sennheiser HD518 or Audeze LCD-2 Rev 2 headphones. This was based on their consistency in seal, low distortion and extended frequency range. They were also circumaural headphones, which are worn around/over the ears, to ensure a constant coupling with the head. Also, the price ranges for both the Sennheiser and LCD 2 headphones varied. The LCD 2 was $995 while the Sennheiser was $125.

Harman’s researchers performed a no EQ test in order to find the curves required for the experiment. EQ stands for equalization. This is the process by which an audio system’s frequency response can be altered by changing the volume or amplitude of its audio signals. He created six models of equalizers after a test that was not EQ. This included their Harman reference room’s frequency response.

These frequency responses are a result of psychoacoustic studies. Harman eventually used two curves, the RR_G (or RR1_G) curves. The RR1_G was a straight line which sloped downwards as frequency increased. The RR_G curve corresponds directly to a horizontal straight line with boosted bass. When listening to loudspeakers, the preferred frequency response was RR1_G.

Harman researchers gathered a group of 10 audio-listening employees and tested each headphone six more times. Each subject was required to give a preference rating of 11 points. Subjects were given the freedom to choose from different frequency responses or programs and could also give feedback. They chose programs and music that had a wide frequency spectrum and high-quality audio recordings to test.

What was the result of the test?

Harman researchers determined that the RR1_G was the preferred response curve for the Audeze LCD-2 headsets. This was in contrast to the RR_G. The Sennheiser HD518 also scored a higher rating using the RR1_G response curve after equalization.

According to the researchers, the correlation suggests that stereo recordings recorded on a stereo system monitor sound better when headphones are equalized as stereo loudspeaker systems.

Researchers found that listeners preferred neutral sounding headphones to be balanced. The least preferred headphone target response was described as being too bright, dark, thin, or colored.

What is Frequency Response and how does it work?

Frequency Response refers to the frequency range that headphones can reproduce. The ideal frequency range includes the range between 20 Hz to 20 kHz. Frequency Response is the ratio of the output of the headphone to its input. This essentially shows how well headphones reproduce each frequency of an audible signal in terms amplitude.

Harman and its research team wanted to find the best frequency response of headphone frequency. At the time there wasn’t much consensus.

Listeners are divided into three groups according to the Harman curve:

  • Harman curve fans: This group is primarily made up of people under 50 years old and represents 64% percent of all listeners. They are looking for headphones that tune to the Harman curvature in sound quality.
  • More bass lovers: 15% of listeners are from this group. This mainly includes young and male people. They prefer headphones that have 3 to 6dB less bass than Harman curves for sounds below 300Hz, and 1dB greater for outputs above 1kHz.
  • Bass is less important: 21% of listeners are females older than 50. They prefer bass below the Harman curve of 2 to 3dB. Outputs above 1 kHz are preferred 1db less.

What are other Headphone Response Curves?

  • Free-field response:

This was made by measuring a flat speaker inside an anechoic room. The sound is absorbed easily in the walls by the latter. A human doll was placed right in front the speaker. Later, the sound was measured by microphones placed inside the ears of the dolly. It turned out that anechoic rooms are not common, so the sound is unnaturally good. This is why the Free-field curvature isn’t very well-liked.

  • Diffuse field response

This response is different because it uses a very reverberant area. Instead of having one speaker, many are placed around the doll. All are flat. It was conceived that sound bounces off surfaces and we can hear it all around us. It also makes it more “natural”. In practice, the diffuse field curve is almost flat with a brighter tone and treble.

How to Describe Sound Localization

Understanding the relationship between human frequency response and sound localization is the first step in understanding the Harman Curve. This will allow you to identify four cues that are dominant in directional localization.

  • Interaural Level Difference (ILD)

Interaural level differences are defined by the difference in loudness or frequency distribution between your ears. Sound travels further and the strength of sound diminishes, so the sound will be weaker at the closest ear.

  • Head-related Transfer Function (HRTF)

Specialists refer the human ears’ response and ability to locate the point of sound from a sound source to be the head-related functionality. Multiparts of your body are involved in the search for the sound source, just like the brain, inner and outer ear.

  • Interaural time difference (ITD)

The interaural difference refers to the sound that arrives in each ear differently. This time difference can be used to identify the source of sound by comparing the paths between your ears.

  • Interaural phase difference (IPD)

Another important aspect of sound localization is the interaural Phase Difference. It refers to the phase differences in sound waves that reach each of your ears. It is heavily dependent on ITD as well as the sound wave frequency.

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