The Terrific HiFiMAN HE400S Planar Magnetic Headphones Measurements

Click on graphs image to download .pdf for closer inspection.

I suggest the reader have a look at the Sennheiser HD 600 measurements along side the HE400S as a reference point.

Raw frequency response plots show a gently rising response from 300Hz to 2kHz, and then a 12dB peak at 3.5kHz with subsequent roll-off to baseline level at 10kHz falling somewhat thereafter. This is very close to the Harman target response and the mid-range coherence I heard is likely a result of this profile. The HD 600, by comparison, shows the raw response actually descending between 300Hz and 1kHz—I think this may account for the "Sennheiser veil" so often mentioned early in the lifetime of the HD 600/650.

Bass response falls of somewhat rapidly below 100Hz and results in the lack of bass weight I heard. Experiments done by the SBAF crowd indicate that the somewhat leaky velour pads are the culprit, and bass response can be improved with less leaky Focus or leather pads. The HD 600 has a similar falling bass response.

Lack of low bass can also be seen in the 30Hz square wave as a significant swayback and loss of height. But it's also worth noting the waveform does not descend much below the zero line, which indicates good phase performance and low distortion. The HD 600 does exhibit a more exaggerated swayback shape.

Speaking of distortion, the HE400S has very low measured distortion. In fact, very few headphones have continuously descending distortion over the frequency range. The gentle rise in bass distortion is somewhat unusual for a planar magnetic headphone; most are fairly flat in this area. However, compared to the HD 600, the HE400S is very well behaved. It doesn't rise above 1% so it should be fairly inaudible.

The leading edge of the 300Hz square wave and impulse response does show a mild ring, and I think this accounts for the slightly hazy or splashy (very slightly) treble. There's little nasty noise in the transient response; very little, if any, harshness is heard. The HD 600, in contrast, shows a longer ringing time and a third hump. I heard the HE400S as having a bit better imaging as a result of better transient response.

Impedance and phase plots are very flat and have little in the way of troubling artifact. The very low 22 Ohm impedance sometimes indicates to me a lack of ability to scale well with better front end gear. Contrarily, I felt the HE400S did scale well with better electronics.

Isolation is, of course, minimal with an open acoustic design. The 0.086Vrms needed to achieve 90dBspl at the ear indicate a headphone that is easily driven by portable devices.

I find these very good measurements for a headphone at this price. Swapping pads for better bass response will make them better still.