Review: HiFiMan HE-400i Planar Magnetic Headphones

The HiFiMan HE-400i planar magnetic headphones lying down flat
Brent Butterworth
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An Upgrade of HiFiMan's Top-Selling Planar Magnetic Headphone

A side shot of the HiFiMan HE-400i planar magnetic headphones
A side shot of the HiFiMan HE-400i planar magnetic headphones. Brent Butterworth

HiFiMan created a big stir among headphone fanatics when it launched the original HE-400. The HE-400, then priced at US$399, was a true audiophile planar magnetic headphone selling for just a little more than a garden-variety, closed-back set of dynamic headphones. Yet unlike many other planar magnetics, it was sensitive enough that you could drive it with a basic smartphone or MP3 player.

The HE-400 turned out to be the best-selling model in HiFiMan's history, but it did feel and look a little clunky. So when HiFiMan created a whole new, much more refined industrial design for its HE-560 headphone, it decided to give the HE-400 a makeover, too. The result is the HE-400i.

So what's different from the original? According to HiFiMan, the new model is "30% lighter than other full-size planar magnetic designs" – a fact that seems about right. The new model also has a headband designed to provide a more consistent clamping force all around the ear, using pads made from pleather and velour.

The HiFiMan HE-400i features a new single-sided planar magnetic driver, designed to deliver tighter bass and better imaging. This seems like a good time to explain planar magnetic to those who aren't yet hip to headphone tech. A conventional dynamic driver uses what's essentially just a little speaker with a voice coil – a cylindrical magnet and a diaphragm that's usually made from some kind of plastic. A planar magnetic driver uses a mylar diaphragm onto which a long wire trace has been applied. The diaphragm is surrounded by perforated or slotted metal panels, which are attached to a magnet. When electricity passes through the wire traces, the diaphragm moves back and forth between the metal panels. Because the planar magnetic diaphragm is lighter than a conventional dynamic driver diaphragm, it tends to produce more detailed, delicate treble.

HiFiMan's innovation was to eliminate one of the metal panels, so the diaphragm is open on one side. In theory, this design should increase efficiency and also minimize the acoustical interference of the metal panel.

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HiFiMan HE-400i: Features and Ergonomics

The HiFiMan HE-400i planar magnetic headphones lying down flat
The HiFiMan HE-400i planar magnetic headphones lying down flat. Brent Butterworth

• Single-sided planar magnetic drivers
• 9.8 ft/3 m detachable cord with 3.5mm plug
• Included storage/presentation box

There's not much of a features list with these headphones. But this is an audiophile headphone designed for home use, so it's not really supposed to do anything except sound super good.

The HiFiMan HE-400i features an open-back headphone design, which means that almost all the sound from your environment will leak into the headphone. The headphone will also leak sound out; it's not loud, but it might annoy someone sitting right next to you.

In terms of how the headphones feel on the head, the HE-400i seems a little lighter than the older HE-500 we have kicking around. But the real improvement is in the headband. The HE-400i squeezes the ear pars around your ear more evenly, so pressure is better distributed. It doesn't feel so much like there's some sort of monster clamping itself onto your head. We wore the headphones for hours at a stretch and never found it uncomfortable.

The presentation box is nice, but we would have liked to have a Pelican-style carrying case for the HE-400i (like Audeze offers with its headphones). Some of us know that good sound can save even the most disastrous vacation.

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HiFiMan HE-400i: Performance

Product box for the HiFiMan HE-400i planar magnetic headphones
Product box for the HiFiMan HE-400i planar magnetic headphones. Brent Butterworth

We liked the original HE-400, but also felt spending an extra $300 for the HE-500 was well worth the money. The original HE-400 had the classic planar magnetic detail and delicacy. But for us, its lower treble was too elevated, and its over tonal balance was too bright. The new HE-400i is far more refined and conservatively voiced, but it can be a much tougher decision as to whether one should spend the extra $400 for the HiFiMan HE-560 headphones. To our ears, the HE-400i and HE-560 are much closer in quality than the HE-400 and HE-500.

We happened to be listening to Led Zeppelin's "D'Yer Mak'er" while testing another headphone, because the snare drum sound on this tune is so singular and full-bodied. The other headphone (the very nice Brainwavz S5 in-ear headphone) didn't quite have the upper-bass oomph to get that snare drum right, but the HE-400i had all the body it needed to.

We just kept on listening. And listening. And listening. The HE-400i is such an easy headphone to listen to, that we actually forgot (on several occasions) that we were supposed to be reviewing them!. Lost in the music of our favorite test tracks!

Not only was the snare drum rendered almost perfectly, we especially loved what the HiFiMan HE-400i did with voices. We couldn't recall ever hearing so much detail and subtlety in Robert Plant's vocals – especially the loudly whispered "fire" at the end. We weren't sure what he was saying there previously.

Likewise, we could hear every bit of breath, every subtle mouth sound in Meshell Ndegeocello's powerful version of Nina Simone's "Four Women." Her voice sounded so clear, yet not hyped up or exaggerated in any way. We were also blown away at how far apart the electric guitar in the left channel and the acoustic guitar in the right sounded. It was as if they were on separate stages at opposite ends of a large dance hall, instead of coming from drivers hanging about 1/2-inch from the ears.

We also noticed that these headphones don't support a ton of bass – there usually aren't with open-back headphones – so we put on something with a solid groove just to see if the HE-400i could keep the rhythm. First we tried "Ritha" from jazz organist Larry Young's great 1964 Blue Note Records debut, Into Somethin'. Yep, the bass notes of Young's Hammond organ didn't sound real strong, but overall we were extraordinarily happy with the sound quality – particularly the incredible detail heard in the brushed snare. We could also hear someone on the recording muttering softly while playing. This is not uncommon among jazz musicians, but we simply never noticed it before in this recording.

We wondered what the HiFiMan HE-400i could do with a real powerhouse tune, so we put on ZZ Top's heavily compressed, highly kick-ass "Chartreuse." We noticed a fairly mild upper midrange/lower treble emphasis. But otherwise, the sound was extraordinary with detailed guitars, drums, and vocals. And as long as you're not looking for big bass, the HE-400i's tonal balance works surprisingly well for heavy tunes like this.

We had a chance to compare the HE-400i to the HE-560 and were happy to hear that both headphones sounded quite similar. we can't say the HE-560 comes across as more detailed, but it does sound more neutral to our ears (with what sounded like a more subdued and smoother peak in the lower treble). Would we pay the extra $400 for the HE-560 (which also has handsome wooden earpieces)? It would be a tough decision for many.

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HiFiMan HE-400i: Measurements

Frequency chart for the HiFiMan HE-400i
Frequency chart for the HiFiMan HE-400i with left (blue) and right (red) channels. Brent Butterworth

The chart shows the HE-400i's frequency response in the left (blue) and right (red) channels. Up to about 1.5 kHz, the measurement is fairly flat, as is typical for open-back planar magnetics. At higher frequencies, the treble response is elevated, suggesting this headphone will sound somewhat bright.

We measured the performance of the HE-400i using a G.R.A.S. 43AG ear/cheek simulator, a Clio FW audio analyzer, a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface, and a Musical Fidelity V-Can headphone amplifier. Measurements were calibrated for ear reference point (ERP), roughly the point in space where your palm intersects with the axis of your ear canal when you press your hand against your ear. We experimented with the position of the earpads by moving them around slightly on the ear/cheek simulator, settling on the positions that gave the most characteristic result overall. Like most open-back planar magnetics, the HE-400i isn't all that sensitive to placement.

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HiFiMan HE-400i: Comparison

A frequency response chart comparing the HiFiMan HE-400i, HiFiMan HE-560, Audeze LCD-X, and Oppo PM-1 headphones
Comparing frequency responses of the HiFiMan HE-400i (blue), HiFiMan HE-560 (red), Audeze LCD-X (green), and Oppo PM-1 (black) headphones. Brent Butterworth

This chart compares frequency responses of the HiFiMan HE-400i (blue), HiFiMan HE-560 (red), Audeze LCD-X (green), and Oppo PM-1 (black) headphones. All are open-back planar magnetic headphones, referenced to 94 dB at 500 Hz. The two HiFiMan headphones have similar responses, the HE-560 showing a little less bass and +2 to +5 dB more energy between 3 and 6 kHz. Both will sound more trebly than the Audeze (which has a "bass bump" centered at 45 Hz and a fairly mild treble response above 4 kHz) and the Oppo (which has the flattest measured response).

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HiFiMan HE-400i: Spectral Decay

A spectral decay graph for the HiFiMan HE-400i planar magnetic headphones
A spectral decay graph for the HiFiMan HE-400i planar magnetic headphones. Brent Butterworth

This chart shows a spectral decay (or waterfall) plot of the HiFiMan HE-400i. Long blue streaks indicate significant resonances. This shows a lot of resonances – actually less in the bass than we're used to seeing, but there's a lot of resonance between 2 and 6 kHz, and another strong one at 12 kHz.

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HiFiMan HE-400i: Distortion and More

A chart showing the total harmonic distortion (THD) of the HiFiMan HE-400i headphones
Total harmonic distortion (THD) of the HiFiMan HE-400i headphones at 90 dBA (green) and 100 dBA (orange). Brent Butterworth

This plot shows the total harmonic distortion of the HE-400i measured at 90 and 100 dBA (set with pink noise generated by the Clio). Even at these very high levels, distortion is almost non-existent. As it has been with most planar magnetics we've measured.

We also measured impedance, which was almost dead-flat in magnitude (at 43 ohms) and phase through the entire audio band. As expected for an open-back, isolation is almost non-existent, with just a slight attenuation above 2 kHz maxing out at about -8 dB. Sensitivity measured with a 1 mW signal between 300 Hz and 3 kHz at the rated 35 ohms impedance, is 93.3 dB. That's pretty low compared to most other headphones, but OK for planar magnetic. We got plenty of volume from an Apple iPod Touch.

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HiFiMan HE-400i: Final Take

A close-up of the HiFiMan HE-400i planar magnetic headphones
A close-up of the HiFiMan HE-400i planar magnetic headphones. Brent Butterworth

We think that the HiFiMan HE-400i is a better set of headphones than the original HE-400 in every single way. We expect some listeners to prefer a more subdued treble and/or a little extra kick in the bass. There may be no better deal in an audiophile headphone than the HE-400i. Although not a low-priced alternative to an audiophile headphone,  the HiFiMan HE-400i is a real audiophile headphone through and through.