We measured and compared the frequency responses of the main mixing headphones on the market. Measurements were made using G.R.A.S 45CC using IEC 60318-1 ear simulator and Dewesoft AD conversion Sirius system.



David will guide you through the process of measuring every single headphone at OLLO Audio. Dive in!
• 0:26 – Standard IEC 60318-1 and
equipment we use
• 1:12 – How we approach measurements
• 1:37 – Measurement process
• 3:16 – How can you get frequency response graph?
• 3:54 – What it all means?

g.r.a.s. and dewesoft


After thorough research and advice from Bang & Olufsen, we went for G.R.A.S 45CC using IEC 60318-1 ear simulator and Dewesoft AD conversion Sirius system. This is a gear used in top research labs like NASA, CERN, Mahle Sound and vibration labs, Spacelink, Airbus, SpaceX, Yamaha, and others.

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measuring conditions

The headphones were all measured in a single day with the same equipment, one after the other, so there would be as little change of deviation as possible. Before every single headphones were measured, the loudness was set as close as possible to 80 dB at 600 Hz using pink noise as the source, reading it's value from the data acquisition system.

The reference environmental conditions were:
Static pressure: 100,3 kPa,
Relative humidity: 33%,
Temperature: 23°C.

spatial averaging

Headphones must be measured in multiple positions to more accurately reflect the acoustic energy in the system. How the sound hits the coupler, at what angle, and how tight the ear pads are, will affect the measurement significantly.

Also, the earphone coupler has internal dimensions that allow modal artifacts to appear. These are like the room modes you try to damp with acoustic treatments in your listening room but occur at much higher frequencies due to the small size of the chamber. These artifacts will move around as the size and shape of the enclosed volume changes with the position of the headphones on the ear. 

compare comparable

There are different variables one has to take into account when measuring the headphones so that the curves can be compared. That's why comparing measurements from different labs, or even reviewers can be very misleading. 

Make sure you have the measurements normalized, and you know for a fact what you're comparing goes together. Compare only one standard and do not do cross-comparisons!



Headphones can't be measured with standard measurement microphones. They have to be measured like they are used - coupled to a microphone that mimics the acoustic characteristics of the ear. So when we measure a headphone, we are trying to mimic what the eardrum hears.

Flat sound in the free field is not flat by the time it gets to your eardrum. This difference between the flat sound in the free field, and the EQ of the sound you hear at the eardrum when you stick your head in the sound in the free field, is called the Head Related Transfer Function.


Many things come into play that affects the EQ of the sound reaching your eardrum:
👉 Your chest and head volume provide some acoustic gain at mid-frequencies.
👉 Between 2000Hz and 5000Hz, the concha (the little cup in your outer ear around the entrance to your ear canal) acts as a focusing dish to get sound into your ear canals, and as a result, provides some significant gain to the signal at these frequencies.
👉 The length of the ear canal provides the opportunity for modal artifacts, typically peaks at 3kHz, 9kHz, and 15kHz roughly, depending on the exact size and shape of the ear.

That's why when we measure headphones, we are not looking for a flat response. Instead, we are looking for a response that is altered in a way a flat response is altered in reality with the anatomy variables. A true flat is different for every individual. We tried to hit the perfect balance to deliver a flat response to as many engineers as possible.


Here is an example of Harman Target Curve on a raw measurement chart without any compensation. Dr. Sean Olive researched that in-depth and published quite some papers on the matter in AES Journals. 

His research empirically proved that the majority of consumers would enjoy about 5 dB boost in the low-frequency area.  Our test with our endorsers shows that audio engineers prefer a bit less in the bass region due to clarity and masking effect that can quickly build up. That's the basis for the frequency response design we undertook with the S4X headphones.

You can see in the charts the low area is slightly elevated, but a bit less than Harman Target Curve suggests. The closest headphones to it that we got our hands on are AKG K371. Very nicely shown in graphs how their target curve is different than what we designed. Keep in mind the research was focused on finding out what consumers consider flat. 


To be able to use measurements in an efficient way, the printed version that comes with the package is not enough. You need to get a curve you can inspect in depth. Measurements for the headphones bought before April 2020 are available in your account. For orders after April 2020, please request measurements via HelpDesk. An excel file will be sent to you, which will provide data for your specific headphones.


The first thing is to adjust the scale of the graph to a resolution that can provide you with some insightful data. In a too broad scale, your response will be just a flat line, that doesn't tell you anything. Zooming in too much will reveal all the little deviations from 0dB, but you can’t really use that as those differences are so small your ears won't even perceive them, and there is no need to complicate your life by compensating for them.

Any headphones have some deviations from 0. You need to be able to see that deviations in parameters that help you do something with them.


In our opinion, a 10 dB scale is the best way to represents how headphones actually sound, offering the most useful view to use in any reverse EQ-ing.

Find deeps and boosts in the curve that ARE greater than 3dB. Find the center of the WHOLE plot. Doing that with your eyes is accurate enough, no need to go crazy with a ruler. :) Then read and reverse EQ if you really wish so get even closer to IEC 60318-1.


So if your measurements have a boost with the highest point on 200 Hz, you should set the EQ to that frequency and cut it down a half step. If it’s a 4 dB boost, you cut it down 2 dB. Also, try using low Q factors below 1. High Q factors will cause more phase issues than anything else. We are intentionally using half measures because of the way speakers acoustics responds to the input signals. If we take the low frequency with a lot of energy out, that would also affect how much harmonics we have left, how much room it's going to be in the ear cup for other frequencies to develop. Do this with all the significant bumps and boosts. Probably 2-3 areas on most headphones.


S4X reference headphones