The HE400i is a mid-range open-back can produced by Hifiman as a successor to the original HE400 and HE400S (though both S and i models were sold at the same time). It has initially known 2 variants : old models with SMC connectors, and last iterations who came with 2.5mm jack on the cups. The Hifiman HE-560 was the higher-end planar based on the same design, while th Sundara replaced both recently.
The HE400i is very comfy, build quality is known to be an issue ; lots of reports of brokean headbands and questionable plastic construction. The currently sold HE4XX is derived from the HE400i. The HE400i has undergone several revisions since its original 2014 release.
○ Release : 2014
○ Current status : In Production
○ Type : Over-ear / Open-back
○ Measured weight : 375g
○ Impedance : 45 Ohms
○ Sensitivity : ~92.5 dB/mW
○ Average used price : $110-140
I quite liked the HE400i, but as soon as I heard other older HFMs like the HE500 or HE5LE, I didnt find the HE400i to be a good performer for the price (back then, which was well above $250).
Overall balance seems fine, with tight linear bass and good low-end extension. Bass is a bit shy in impact and I would like a bit more slam. Midrange is just a tad dry and distant for me, not too full between 1 and 4 khz (a common trait with lots of planars headphones).
Treble is where issues started ; most Hifiman headphones have a forward treble and this one is no exception. It’s quite strong around 8-9khz, and a bit grainy. The HE400i and DT880 highs sounded similar in treble quantity when I compared them.
I found the staging coherent, not too wide but not narrow ala HD600 or most closed-back. While it has good speed, it lacks the punch and “weight” of the HE500 (I did compared them side by side for a long time). I prefered the HE500 and sold the HE400i.
The latter is now around $100-150 used, a considerable depreciation considering the original $499 MSRP. The 4XX is not an horrible value at $170, but I definitely recommend the HD6XX instead. Or stretching up the budget and buying a Sundara, which is a much better sounding headphone than the HE400i/HE4xx.
Measurements & Resources
Frequency response looks quite decent, although the midrange is slightly more dipped than I’d like, especially around 2 kHz, and the treble is simply too elevated from 6-7 to 10 kHz. Bass extension is quite solid.