Pros: very detailed warm neutral sound which is fun to listen to!
Cons: bass (I know its neutral and I shouldn't have high expectations for it :))

Arrived in a very elegant package, this "waterline" labeled RE-400 model looked very sharp. Just like with HM700/RE-400B, a lot of attention was paid to presentation of the product to the point where they actually had to include the storage hard zippered case with extra eartips in a separate bag so it doesn't interfere with a slim profile of the original RE-400 package. The headphones were sitting inside of a felt lined foam insert with cutouts for extra eartips. Furthermore, more eartips were included with a storage case. When it comes to accessories, HiFiMAN never disappoints. In addition to headphones and storage case, they included 3 pairs of bi-flange eartips, 2 pairs of smaller black silicon tips, 3 custom shape clear silicone tips, 2 pairs of T-400 Comply premium foam tips (large and medium size), 5 pairs of filters, and a shirt clip. Though I can tell you ahead these headphones sound amazing, the right selection of eartips is VERY important to bring out the best in sound and isolation. I have a rather large ear canal and always use the largest included tip, where the custom shaped clear one provided the best passive noise isolation I ever experienced with any of in-ears.

The first thing you notice when you take these headphones out - how super lightweight and compact they are. The barrel of these earpieces is made out of lightweight aluminum material and has a great ergonomics to fit comfortably inside of your ear. The barrel opening is covered by a cloth material filter (5 replacement pairs included), and right next to the strain relief there is a pinhole port for sound shaping. Followed by a decent strain relief the cables use a durable shiny rubber coating up until the y-splitter. Included chin slider moves very smoothly and made out of the same aluminum material. After y-splitter, the cable has a "shoe lace" type of cloth material cover which is still very durable and doesn't have that annoying springy effect found with so many other cables. The cable is terminated by a gold plated 3.5mm angled connector with a flexible strain relief. I also noticed microphonics effect was down to minimum.

When it comes to sound quality, RE-400 delivers amazing results! This single dynamic driver in-ear really focuses to deliver a neutral transparent sound but unlike other neutral headphones that sound lifeless - these are very smooth and warm. The sound is not in your face, it's a few steps back, but it sounds very natural without any artificial enhancement. The characteristics that surprised me the most was the low end where neutral headphones usually try hard to show details but lack the extension. Here, you still get a very detailed bass sound without any humps, but it actually extends beyond mid-bass punch down to some sub-bass texture. It's not enhanced or boosted, just perfect to enjoy your low frequencies, well controlled without spilling into mids. I found bass to be not as fast in comparison to my other headphones, but it's very well rounded and full. Mids are very detailed, clear, maybe a bit forward but not too much. The vocals sound very natural and lush. High frequency (treble) is extended, detailed, bright but not harsh and without any hint of sibilance. Upper mids/treble is very well controlled and just perfect for extended listening period without ear fatigue. The soundstage is average, not too wide which was definitely a step back from RE-400B balanced version that had an amazing 3D width. But this is in-line with other similar IEMs, while balanced wiring/architecture is intended to widen the sound. The headphones were really easy to drive from my phone and X5, but I did notice I had to dial in a higher volume level to enjoy them more.

Overall, I knew that I will not be disappointed with RE-400, and my testing just solidified that! No matter what genre of music you are listening to, these headphones will guarantee to bring out the best in every song. The sound has just a perfect balance of neutral natural tones without going into any extreme. Perhaps if you are a basshead craving for a more bass impact or need an analytical bright set of headphones - these might not be your cup of tea. But as all around headphones that sounds and looks great, and has a very reasonable pricing in comparison to other single and multi-driver IEMs in the sound sound category - these deserve a serious consideration.

Here are the pictures.