November 2017 Update: I made a revised version here.
Use the files in the Download section below to give your HE400i a neutral frequency response. It sounds good.
My first attempt at developing an equalizer setting to flatten the HiFiMan HE400i‘s frequency response yielded excessively elevated 8KHz and 10KHz regions. This is because I used InnerFidelity‘s measurements. They are consistent among themselves, but the Hammershøi and Møller HRTF curve that I used for frequency response compensation is inappropriate for Tyll Hertsens’s Head Acoustics HMS II.3 head simulator, so the compensated frequency response was a off in the treble.
This time, I asked Solderdude (administrator of DIY Audio Heaven) for his measurements of the HE400i made with his home-made measurement rig. Although Solderdude’s device is not a calibrated HATS, I find his measurements to be very accurate.
Measurements and Correction
(The corrected graphs are predicted/calculated results instead of real measurements, because I don’t have access to Solderdude’s measuring equipment, and Solderdude no longer has access to an HE400i.)
Solderdude’s measurement shows the very audible 8KHz peak that InnerFidelity’s graph didn’t show. According to the graph above, the corrected frequency response is ±1dB from 20Hz to 13KHz, but the actual effect will be different for each person using this correction due to individual HRTF differences. However, an approximately neutral frequency response is assured.
Since frequency response and impulse response are interrelated counterparts of each other, modifying the frequency response using an equalizer inevitably changes the impulse response. The corrected impulse response has less reverb and is more ideal.
This is a graphic representation of the parametric filters. Extremely sharp boosts and cuts are avoided.
- Bass extends better.
- The 8KHz sibilance edge is gone.
- Soundstage has expanded and imaging is more precise.
- Voices are less muffled.
On Equalization Methods
Impulse response convolution appears to be the highest-quality, most versatile and most customizable method of frequency and impulse response correction. I tried DRC (Digital Room Correction) by Denis Sbragion on the HE400i, but I chose to use Room EQ Wizard instead for the following reasons:
- DRC cannot avoid automatically correcting the >13KHz region of unreliable measurement data. This could make the sound worse than it originally was.
- DRC tries to extend the bass way down below 10Hz, causing unnecessary subsonic rumble.
- DRC shows no significant quality advantage over REW in this case of headphone measurement.
- Convolver wave files – stereo 24bit 44.1KHz – 192KHz.
- Equalizer APO config txts.
- If you want to use other parametric equalizers (not recommended), refer to the values in these configs.
- Room EQ Wizard REQ file if you want to modify my equalizer setting to suit your taste.
- Graphic equalizers are not supported due to their fixed-frequency/bandwidth nature.