This and That:
The plastic packaging looks cheap, but whatever. What I find really incomprehensible is that the RE400i comes with many pairs of silicone tips, but they don't seem to follow any real pattern and 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. HiFiman did exactly the same thing with the much more expensive RE800 and RE2000, and I can only shake my head about that - almost every other manufacturer manages to include a logical selection of ear tips with their in-ears.
Well, the included tips are admittedly good in quality and texture though, but I can't see a really logical and comprehensible pattern. Instead, the selection seems rather arbitrary.
In addition, there is a round storage case in the packaging, which, like the RE800, is simply any unbranded Chinese case and doesn't even have a single HiFiman logo.
The cable of the RE400i is also rather a bad joke, looks cheap and can't be described as flexible. Strain relief is also used rather sparsely and there's no chin-slider either. On top, it's 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 center 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 RE400i without any defects).
Sound:
I'm lucky that the included large bi-flange silicone tips fit me well and that I can insert the in-ear shells quite deeply with them.
Tonality:
The RE400 is regularly said to have a slightly brighter sound than neutral; however; this is however not really the case, at least in my ears (if the in-ears are inserted correctly and rather deep, and I am definitely not alone with this opinion, as the results of my research confirm). In fact the HiFiman has a rather warm, "balanced", smooth presentation and interpretation of "neutral".
Compared to an in-ear that is diffuse field neutral in the bass, like the Etymotic ER-4S/SR, the RE400 has a boost of about 5 dB (the peak is reached around 90 Hz) in the lows, which gives it about the same amount of bass and lower fundamentals as my InEar StageDiver SD-2, Pai Audio MR3, Logitech/Ultimate Ears UE900(S) or the Etymotic ER-4XR. It has a pinch more bass and warmth than the Shure SE425 or the UERM and UERR and can be characterized as mostly subjectively neutral with a little warmth "on top". If you are not looking for a neutral in-ear, which is the case with most people who are looking for an in-ear in the price range up to $100, the RE400 is the wrong choice.
Low male voices get a pleasing, discreet to moderate warmth through the moderate low-frequency boost, and the lows, which also don't really roll off towards the sub-bass, get a balanced impact, but by no means boring, or, what would be the opposite, a grumbling, thick impact. As far as the tonal tuning in the bass (and also in general) is concerned, HiFiman did a good job with the RE400.
The midrange of the RE400 is pretty well done by HiFiman and presents itself largely without colouration, with just a subtle lift in the upper midrange that helps high female voices and instruments like trumpets to get slightly closer in the mix without really negatively shifting the tonal balance or the timbre (voices have only a very mild hint of brightness in the upper midrange).
The HiFiman's treble is tuned to be a tad more in the background, so that the in-ear delivers an unobtrusive presentation in a positive sense and gets by without any significant, sudden, narrow dips or peaks.
In general, I think my RE400i is mostly comparable to my InEar StageDiver SD-2 when it comes to tonal tuning, but with a few small but significant differences. Both have a similar implementation of the mild bass boost, but the HiFiman is a bit less full than the SD-2, which makes it sound less warm and direct than the German Dual-BA in-ear. In the upper midrange, the RE400 is somewhat brighter than the InEar. The SD-2 is a bit more relaxed in the high frequencies than the HiFiman that is closer to the neutral target curve.
In comparison, you could say that the SD-2 sounds a bit warmer in the low and darker in the high frequencies than the HiFiman.
Due to the even, balanced-to-neutral tuning, the HiFiman sounds "real"/authentic and represents instruments and voices realistically and without colouration or unnaturalness - great!
Based on its tuning, "harmony" and evenness, I think that the RE400 is definitely and quite simply worth its RRP of more or less $100 (and that I can be lucky to have bought a new, unused unit in a sale for a price that was quite a bit lower).
Tonally, the RE400 is, in my view, clearly superior to the more expensive RE800 - because even though the RE800 is closer to the diffuse-field target curve in the low frequency range and conveys less warmth than the RE400 that is priced more in the entry-level range, the RE400 is much smoother and more even above 1 kHz and has the more correct timbre in the treble (an in-ear with the RE800's lows and mids and RE400's highs would be quite perfect).
Resolution:
In a nutshell, the RE400i also doesn't have any real weakness in terms of technical performance and sounds pretty tight, nimble, precise and resolves well for an in-ear that relies on one dynamic driver prt side. The HiFiman's RRP of about $100 is also justifiable in this respect and the in-ear plays at this level, but definitely not above it.
The speech intelligibility of the RE400i is good, which also applies to its general detail resolution and note separation. Concerning the detail resolution and technical performance, the HiFiman is also able to rival good single BA in-ears in the sub-$100 range in most areas and delivers an overall somewhat more precise presentation than some other in-ears with dynamic drivers in the range up to $100.
It's definitely not at Etymotic levels (based on the ER-4 series) though, and also my Fostex TE-02, which is even a bit more neutral than the RE400, is technically somewhat ahead (mainly in the bass which is a bit faster and tighter on the Fostex compared to the HiFiman - because even if the HiFiman performs well in this matter and plays rather cleanly, it still doesn't completely remove the somewhat soft texture of a typical in-ear with a dynamic driver on each side, although it admittedly remains pleasantly precise and controlled for what it is).
Soundstage:
The HiFinan presents an imaginary space that is a bit wider than deep and doesn't present itself as very small or very large - overall it's quite average and not as open as one might be used to from some other in-ear with a single dynamic driver per side.
As far as width is concerned, the HiFiman plays exactly in my head according to my perception and does not leave the base between my ears.
The locating sharpness and instrument separation, on the other hand, is quite good.
Conclusion:
As far as the tonal tuning is concerned, HiFinan hits the nail on the head with the RE400, a largely neutral to balanced, very natural sounding in-ear with a pinch of warmth and relaxation. So those looking for a balanced in-ear that goes in the neutral tonal direction and delivers good technical performance can't really do much wrong with the RE400 in the sub-$100 price range.
But what the Chinese company thought about the cable and the included ear tips remains a big mystery for me, since the selection doesn't make much sense. The cable is not great either and the fact that the remote control's volume buttons don't seem to work as they should are a bummer, too.