HiFiMAN RE-400

General Information

The RE-400 Waterline by HiFiMAN is a premium quality, high-performance In-Ear Monitor (IEM) that sets the standard for others to follow. Featuring advanced ergonomics for superb fit, and premium materials such as Titanium Diapharagm, Neodymium magnet and OFC Copper cabling, RE-400 represents best-in-class performance and comfort.
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Latest reviews

CK Moustache

100+ Head-Fier
Link to my review and measurement index thread where one can also find a full review overview, more information about myself as well as my general-ish audio and review manifesto: https://www.head-fi.org/threads/956208/

HiFiMan RE400i


Personal unit.


Plastic packaging appears cheap, but that’s okay.
Ear tip selection doesn’t seem to follow any real pattern – while many different pairs are provided, they sometimes differ considerably in length and properties; it would have been much better and more logical to include three different sizes of tips for each type of tip. Quality and texture is good, though.

Round storage case that is simply just an unbranded case without any logo. Protective, though.

Cable feels and looks cheap; cannot really be described as flexible. Strain relief not good and no chin-slider either. Quite microphonic.
The three-button remote control has a pleasant pressure point. Although the individual keys are not so easy to recognize as such haptically, it's still quite easy to distinguish the two volume keys from the centre key due to the size of the remote control. What I don't like so much is that the remote control is located on the left side. By the way, I also doubt whether the remote control is actually mfi-certified, because on my Apple iPod Nano 7G, the volume buttons remain without function after being pressed twice, no matter for how long, until I remove the in-ears and plug them into the jack socket of my iPod again (that even though I’ve got a genuine pair of RE400i without any defects), and on my Apple USB-C to Headphone Jack Adapter, a short press of the volume up button results in an irreversible maxing out of the volume.

Shells made of metal. Look very nice. Their build quality is good.

One dynamic driver per side.


Largest included black dual-flange silicone ear tips.


Fairly neutral leaning somewhat towards the warmer side.
Actually quite comparable to my InEar StageDiver SD-2 but with a brighter/less dark upper treble response.

Mild to moderate warmth in the root with the bass’ maximum quantity reaching around 5 dB in quantity above flat neutral at ca. 100 Hz in the upper bass. Flat extension into the sub-bass.

Ultimately a bit of warmth in the lower mids but not as much as my SD-2.
Flat central midrange with slightly reduced presence range but in the end still correct and neutral timbre.

Treble on the smooth and neutral/slightly darker side with a mild lift in the upper highs that ultimately leads to cymbals not always sounding sounding right but somewhat artificial/metallic. Never sharp or peaky.

Overall smooth, heading into a neutral direction and pleasant. Ultimately not as even as Etymotic’s in-ears but still some of the very best neutral-ish tuned dynamic driver in-ears regardless of price.

Perhaps the highs are brighter with shorter ear tips and/or a shallower insertion.

Frequency Response:


To my ears, there is no such elevation in the highs but just a mild lift.

ProPhile 8-Compensation


Decent but nothing that’s outstanding or special.

Somewhat on the softer/slower side without really becoming muddy. Would still be appropriate for the ~100$ original price and is clearly nothing to worry about when purchased at around half of that or below; good value.

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Compared to the Etymotic ER2SE:

Apart from the bass and root, the two are tuned quite comparably neutral, with the ER2SE however still taking the lead in the end due to their higher treble linearity and evenness (my RE400i are a bit more forward in the lower upper and upper highs, with comparatively more metallic, less realistic sounding cymbals compared to the Etymotic).
In the bass and root, the HiFiMan have got an elevation that is stronger than the ER2SEs’ by around 4 dB, which makes them sound bassier and warmer (therefore their tuning would be more comparable to the ER4XRs’).

The HiFiMans’ bass texture is softer compared to the Etymotic, and the ER2SE sound somewhat tighter in the lows, too. The Etys’ bass control is superior.
In terms of resolution, I see the ER2SE one or two leagues above my RE400i – they just sound cleaner and their minute detail resolution is higher, just like their speech intelligibility and note separation in fast and busy parts of the music.

The ER2SEs’ soundstage appears larger than that of my HiFiMan in direct comparison, especially in terms of spatial depth and three-dimensionality, while the spatial width is more or less comparable.
The imaging (instrument placement and separation) and especially the portrayal of “emptiness” around and between instruments is more precise on the ER2SE.


Smooth, neutral-ish sound that is heading somewhat into the warmer direction.
Rather “typical” dynamic driver technical performance but not muddy yet.
Cable could be better, just like the ear tip selection.


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New Head-Fier
A close to ideal IEM
Pros: - Absolutely distortion free no matter the volume
- Stellar imaging
- Smooth frequency response
- Very easy to EQ thanks to the many measurments available online
- Small and confortable
- Simple yet elegant designe
- Plenty accessories
- Can be found cheap nowdays
Cons: - Tuning out of the box is.. debatable
- The cable is not the most-well behaved
- Need to be inserted faily deep into the ear canal to achieve high frequencies linearity

I got those IEMs for 35€ at my local store. I have no interest in making good advertising for the brand. I only share my opinion hoping some find it helpful. I also aim at supporting/disputing existing measurments and consensus with subjective impressions.

What I'm lookink for: I believe EQ is the cheapest, quickest and more accurate way of achieving excellent audio quality with IEMs. This is why the ideal IEM should have virtually perfect electro-acoustic properties before anything else.

What I listen to: Wide variety of music, but mainly jazz, guitare oriented genres and modern mainstream pop & hip hop. Few classical tracks that I know well for reference purpose only.
I also use IEMs as a chirurgical tool when recording/producing, Occasionnaly for field recording (Etymotics are best for that).

Sources: 192 kbs ogg/ 320 kbs mp3 made from CD quality flac files or CDs on Rockboxed FIIO M3K/ Thinkpad x230 under Debian using Pulseaudio Parametric Equalizer and MPV.


It's surely not the most well built IEMs in it's pricrange. No flashy designe here... Just super discreet and simple. I like that. The lack of mmcx interface is a drawback though, and I don't really like the cable which lacks flexibility and sometimes gets on me nerves.

Tips: A lot of different types of silicon sleeves ar provided which is very nice. The small ones with waxguard gave me the best and most confortable fit. They allow deep insertion which is beneficial in this case. Sound isolistion was sufficient in most everydaylife cases, but pretty far from what an etymotic offers.

Sound: I see no drawbacks technically speeking. Well extended distortion free behavior is clearly shown. It feels almost unreal when turning the volume up. That is a sensation very specific to IEMs. The driver is extremely well damped, it feels precise and capable in very satisfiying way. Listening carefully really gives credit to innerfidelity and Rin Choi's Measurments. Just perfect.
Now tonally, it's quite off. The tuning makes it sound bloated, it severly lacks clarity. It's not unpleasant, but it cannot really be called neutral. It pretty much kills the chance to make it sound realistic and spacious. But you might like it, I have to admit I turn off EQ from time to time for a relaxing mellow ride.

When EQed: You'll have no trouble EQing to diffuse field or Harman target, or whatever sound profile you want. I personally use the Diffuse Field target a lot, it really manages to trick my brain, even slightly better than the Etymotic target (even if they are veeeeery close). These IEMs reacts per-fect-ly to whatever filter you apply to it: A perfect minimum phase system that can even handle pretty hardcore boost. Balanced armature based monitors or things like the Etymotic MK5 which uses an helmotz resonator as a tuning trick typically don't welcome EQ that warmly. In the end I found myself with something just as good as the ER2XR, even less distorted.

Conclusion: I just don't need any other IEM for my every day music enjoyment. If you're ready to experiment with EQ and elaborate a sound profile that matches your personal Head Related Transfere Fonction, it's just a perfect base to build upon. It's price point is very low now, and it can deliver pretty much everything the IEM world has to offer (perfect electro-acoustic behavior which translates into perfect "imaging" and cray amount of "details").
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Pros: Affordable
Cons: No bass
Treble peaks - sibliance
Response far from flat
Cheap cable
Bought them for $47 for my mobile believing the measurements used for full sized cans will have the same indication to real performance but found out the hard way the measurement don't apply the same way for IEM's - see this thread.

They aren't that much better than any Chinese $15 IEM. There are no free meals and to get quality looks like you'll have to be ready to part with $100 or more.
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100+ Head-Fier
Just wanted to point out that these are now on sale at both Amazon and the hifiman website for $20. I personally slightly prefer the LG F-631 Quadbeat 3 "Tuned by AKG" for most uses (which is $15 on ebay, shipped from China), and I EQ the 2k bump down a little. I think I've been through 5 pairs of those over 3 years as I'm sometimes careless with my IEMs. However there are a couple of applications where I cannot EQ it, and I'd rather than these RE400 for those times.