PerformanceHiFiMAN has put a lot of effort into the design of the RE-400, and it has payed off in so many areas. First of all, the fit is heaps better than what we are used to from the older models, which helps tremendously with the sound quality of in-ear designs. The fact that you get a marginally better seal gives a more-than-marginal improvement in sound quality. Wearing comfort has also gone up quite a bit because the new tips are more ergonomic, but also due to the different housing design - the less microphonic cable is just a bonus.
The in-ears were tested with the following gear: Samsung Galaxy S3 (International Edition), iPhone 4, and JDSLabs O2+ODAC DAC/amp.
The only issue with the RE-400s is due to the tips: they are comfortable to wear, but the sound quality with them is a bit lower than with a set of dual compound tips that ship with Sony, RedGiant, or many other higher end in-ears. This is a minor issue, as they are very cheap to source online, but we would have preferred these in-ears to come with a set of tips that match their performance.
The RE-400s supersede one of the most influential in-ears in the midrange price segment - namely, the RE-0s. The RE-400s have been introduced for the same price as the RE-0s after two years on the market, which bodes well for the price/performance ratio of these in-ears. The good news is that the RE-400s definitely sound the way HiFiMAN wants them to sound; however, they are tuned more like their bigger headphones - the emphasis is on creating a slightly warm midrange and producing a tight and well extended bass. The RE-0s sound great, but their at times slightly exaggerated treble can be a bit annoying, especially on modern recordings with subpar mastering. The RE-400s have a slightly less sparkly top-end and the upper midrange is even less sibilant than that of the RE-0s, which is a major plus.
The RE-0s thrilled us when they were released. A multitude of very good in-ears in the sub $150 range were launched within the last five years since then; however, the RE-0s kept their attractiveness because of HiFiMAN's aggressive pricing strategy. HiFiMAN is now clearly starting anew with the RE-400s, which is very interesting to audiophiles and music lovers alike. The RE-400s, like the RE-0s, boast tremendous control of the midrange and are even smoother sounding. Their sound stage has also been improved vastly over the RE-0s and RE-262s. The detailed midrange coupled with a very coherent sound stage makes the RE-400s very entertaining to listen to, and it is immediately apparent that the RE-400s are in a different league than the RE-0s. Listening to quality masterings on the JDSLabs O2+ODAC showed an amazing display of midrange control and sound-stage definition that almost made us forget the fact that they were in-ears. They are much better at conveying depth than any of the RE-series earphones preceding it, which gives them a more "out of the head" sound stage.
A lot of bass was never the older RE-series earphone's strong point, and the RE-400s are no different. They have more bass than the RE-0s and the RE-262s, but it is marginal compared to both Sennheiser CX300s and RHA MA350s. The bass control and extension is still ahead of the rest, but it is, amount-wise, struggling to produce enough low-end grunt.
The new RE-400s are very smooth across the range. There are no nasty peaks and the bass, midrange, and treble seem very well-integrated. This is probably one of the reasons why every little detail is conveyed so beautifully. The midrange is simply fantastic and has a level of smoothness and detail you used to pay over $300 for. The new RE-400s are very natural sounding and the low-end reminds me of less powerful Westone ES5s. If you want a lot of bass, there are other options for you. These in-ears are still catering to those looking for a true to life reproduction of the music.
The detail level you get with the RE-400s is rivaling that of much more expensive sets, like the Westone 3s and the midrange offerings from Phonak. The fact that you can get such an experience for $99 is just absurd.