Heh, I might go contrary to everyone, and say that me, and another person at FA, find the westone um3x be the best all-rounder armature headphone. Not in stock for sure, but not a huge overhaul either - it just needs good cable and good eartips. Then it can compare directly to UM miracle (thats the best armature unit we tried to directly compare it with).
Westone 4 is a fail from pure sound quality view, but must be pretty profitable, as it is very cleverly tuned to average people desires and source (which is very important factor also).

Heh, I might go contrary to everyone, and say that me, and another person at FA, find the westone um3x be the best all-rounder armature headphone. Not in stock for sure, but not a huge overhaul either - it just needs good cable and good eartips. Then it can compare directly to UM miracle (thats the best armature unit we tried to directly compare it with).
Westone 4 is a fail from pure sound quality view, but must be pretty profitable, as it is very cleverly tuned to average people desires and source (which is very important factor also).

Hey thanks for sharing my views on the two Westone products!

My UM3X is using a OCC SPC cable and using the stock (new tips) long silicone tips. With the UM3X being on the dark side, I find that Comply tips doesn't necessarily "aid" the treble.

RE-400 is dark, that's why it's stock "mid-fi". The linear error is too much in the highs, ~10 dB dark, but it's almost a plain shelf - little peaks, one notable (to flat) around 4kHz. No ringing, no distortion, easy to drive, not slow bass, very even decay. You need a really, I mean really deep fit with those for best results - on par with Etymotic ER-4. I insert them as deep as possible with short soft biflanges. Long ones "stick up" when put this far, the single flanges can't seal that deep, even the large ones. The angled ones work, but not perfectly - sometimes lose seal.
RE-272 damper only makes them slightly less dark, 2 dB or such, but in the right places - at throughs but not peaks, and at air.
Once the darkness is removed by equalization, they show their true quality.

HE-500 has bass emphasis (actually 2nd order distortion) with stock pads, better with jergpads-style pads which is what I'm comparing to. RE-400 bass is better still, but unless you make them not dark, there's comparatively too much of it.

B2, of which I've just received a new pair, is closer to ideal in FR stock, but it is noisy/gritty in mids, highs, less extended up (manifests as slight lack of air - compensated with general highs boost) and slightly subbass depleted. The 6k peak is there, but now with the best tips I can reduce it to much lower levels (3 dB or so) without making them unbearably dark - using RE-272 long tips with an additional silicone tubing inside to make them fit the narrower nozzles (let's call it an adapter).
They go slightly less deep than RE-400 - "hum test" is resonant but in nose, not ears. With RE-400, there's nearly no resonance at all in this test.
(More edit: actually, the funny medium hardness VSonic olives work as well or slightly better - with the same adapter.)

Hum test: put the IEMs in, hum a low tone, 200-300 Hz. Note where you hear the resonance and how much. Best results are usually when there's nearly none and it's in the center of the head. This measures free air volume in ear and ear canal compliance. Too deep or occluded fit presents with zero resonance on the affected side and obviously low efficiency and "flat" sound. Bad seal presents with little resonance placed very much in ear, sometimes piercing sound, large subbass drop. Shallow depth, but good seal (1st bend) presents with most resonance, located in ear. Often midbass boost and resonance around 6k.

I'll do that soon enough. The difference isn't that huge - better than no damper or stock one - less peaky. The foam should be kept. I've only removed and reinserted it to relieve any possible too thick or uneven packing - this can sometimes happen.

Rin has measured RE-400 in many configurations (w/ and w/o foam, damper, foam + damper and with microfibre) but not this one. He's also unnecessarily applied a vent mod - that is only relevant for shallower fit - perhaps a super deep fit actually occludes the vent somewhat already - at least to my ears. Or actually the Olive-Welti compensation is better than IEC diffuse field.

RE-400 (also RE-0, RE-ZERO, RE-600) dampers are made out of loose cellulose fibers, RE-272 (also RE-262) ones are made out of fine plastic mesh, presumably nylon. They have different sonic properties.

Both kinds can be ordered with respective Hifiman tip sets.