Pros: Sound, Sound, Sound, Comfort, Isolation
The RE-400 is quite easy to drive, but not the easiest. Better than the 64ohm RE-0, but like other 32ohm phones I owned, these need some extra volume to sound better and a bit more to shine. No amping is needed, though.
The new RE-400 is not just an improvement in design, fit and isolation but especially in sound.
The overall sound is neutral with a small added amount of warmth, which gives a fuller sound and better balance through the whole frequencies. Nothing is overpowered, nothing is missing.
Starting from the low-end.
These are NOT for bassheads or for anyone looking for an explosive, earth shattering Bass. But what the new Hifiman offer is a much fuller low end from mid-bass to sub-bass that the previous models were really lacking. While they lack in impact, they still manage to give quite a rumble.
As for the bass quality, it's what you'd expect from Hifiman, SUPERB. Quick, very tight and accurate. You can hear (and feel) every beat, every punch and every kick. Just amazing. Quite fast, but still not the fastest. The ATH-CKN70, for example, showed a much higher speed (well, those aren't just a simple dynamic driver earphones).
Jumping to the high-end. Treble has a good extension with some extra brightness, but remains smooth and non-fatiguing even at a higher volume. While it may not have the 'endless' extension as the RE-0 (it may be closer to the ZERO), it is full, energetic. There's a lot of micro detail as well, not unlike as its predecessors.
And, finally, the midrange. Now, this might be the best part of the RE-400. Just BEAUTIFUL! As simple as that.
As stated before the whole sound is very neutral, but the mids are sweet and just slightly forward, but not thick enough to fall in the mid-centered group. Everything sounds very natural, detailed, transparent and open. Nothing recessed or missing, but the opposite, immersive and addictive. So effortless!
When it comes to more complex music, the RE-400 handles everything with ease, rivaling, and even beating, some good Balanced Armature IEMs.
Vocals need a special mention here as they're even a bit more forward than the rest of the sound. Also, vocals need a bit more time to 'break-in', as they can sound a bit weird (unnatural) and not well-positioned at first. After that, they sound as great as vocals can sound. Every word, every letter can be heard, be it with male or female, main singers or backgrounds.
Soundstage is not too wide, deep or high, but the whole sound has a fair 3D effect.
As I wrote above, I found the small bi-flanges to provide the best sound out of the RE-400, so everything up to now is based on that setup.
Now, I'd like to mention some differences noticed when using the Big Bi-flanges.
When switching to the larger, wider bore tips the sound change as well.
On the whole, the sound remains similar, which is open and detailed, but the presentation is a bit different. The bass has some bigger and deeper impact, but is also not as tight as before. The highs are brighter and extend even further.
But what suffers the more is the midrange, sounding less forward and less sweet, but on the whole is has a better balance.
[And for those who find the stock big tips too big, some aftermarket eartips can give a similar effect]
In either configuration the RE-400 is very versatile when it comes to music genres. They don't excel in something particular, but don't lack either.
Still, those who listen to electronic, EDM, trance/techno and similar music may want to look somewhere else.
In short, one of the best All-arounder IEM, very detailed (but not analytical), airy, well layered, immersive and engaging sound.