A month has passed and I have listened and compared quite a bit, so hereās my review of the he400se.
As reviews are so subjective anyway Iām just going to lay out my thoughts in a simple way using the adjectives that match what I hear.
I found reviews for this pair to be divisive, and mine is as well, my perception doesnāt quite match everyone else, Iād say resolveās review is the most similar.
TLDR
Iām gonna throw my conclusions right off the bat.
If you are relatively new to this hobby or/and want to try a planar, this is an absolute bang for your buck, great for music, gaming, movies and immersion. But beware they need a powerful amp to deliver good bass, at least 1watt at 25ohm should do.
Build and comfort are very nice for a hifiman, they look and feel way better in person than they do on camera, but the cable is shit.
Get a replacement cable, the stock one sets a new standar for shitty cables, cheap amazon cables (newfantasia, geekria, neomusicia) do the trick no problems.
I myself, returned these headphones to amazon, owning several better ones these didnāt sound different enough for me to keep.
Mods (grill, pads) didnāt improve the sound at all to me, in fact they sounded not as good as stock.
Sound overview
Very nice bright tuning, goes in line with the other hifiman products Iāve heard, so this is a nice one to get to know their house sound.
Regarding the frequency response I find it to be linear as the charts indicate, enough bass to be fun, present mids and bright treble, if there is sibilance in the recordings this will produce that sibilance, if you listen to RHCPās californication you will get a bad headache.
Detail is very good for the price, but its not a detail monster by any means. They are fast sounding like other planars, great attack and decay. I would have liked more body in the midrange, other than that I didnāt have any issues with their sound.
These are some of the airiest headphones iāve heard (this is a good thing for me but may be rough for some ears), the vertical soundstage also sets new hights in this price range, the horizontal soundstage is kind of āaverageā big, overall soundstage size is large but the horizontal staging limits how big they sound.
Even though they are bright and have a some heavy air to them I could use them for long periods without any problems.
Gear used
schiit magnius - only this one drove them properly, they sound the same to me from the single ended and balanced outputs.
ifi zen dac (balanced out)
fiio btr5 (balanced out)
With every amp the sound signature is about the same, the coloration doesnāt change very noticeably, but the bass delivery is sloppy on the lower power amps compared to similarly priced headphones.
Comparisons
Sennheiser are A/B, hifimen are from memory, as I donāt own them anymore. I wish I could A/B them but I do trust my memory.
he400i (previous version, not 2020): I find the he400se to have a better, more linear frequency response, overall more true to the recordings, but the he400i were just a little warmer and more fun, thicker and forward sounding, with just slightly bigger horizontal soundstage and lesser vertical size.
sundaras: are basically an improvement in most aspects, but not by a lot. Where its really noticeable is in the midrange (actual body, he400se mids sound thin in comparison) and overall detail/extension. I find them to be a worthy upgrade.
The he400se do have some perks, they respond better to EQ, have punchier bass, and are probably more honest to the mixing, sundaras have some kind of makeup on their tonality and weird staging on some records.
anandas: are almost identical in FR to the he400se, but have a ton more detail and bigger soundstage. However, I find the he400se (and sundaras) to be more dynamic, present sounding.
senn hd560s: I like the sennheisers just a bit more, they are kind of a sidegrade, I love how they stage the instruments horizontally, the midrange and bass have more body and punch (vocals really kick he400se ass), plus they are very easy to drive.
The he400se have a little better extension on both ends, more refined treble, are more immersive (and maybe even more fun), I would pick them for gaming and movies, but they are less musical to me.
senn hd6xx: They sound so different and get colored so much by the source they maybe not worth comparing, what I can say is that hd6xx are intimate, warm and very dynamic, which are things the he400se isnāt.
Pad rolling
My expierence pad swapping the he400se is that its sound doesnāt change very much from pad to pad, I couldnāt A/B them as the pad swap is kinda slow.
I mostly tested them rolled with zmf ori suede pads, they sound almost the same but the sound feels just a little more tight overall, with decreased bass ārumbleā. Comfort is just a bit better.
Specially on longer listening sessions its very hard to tell the difference from stock.
Other pad rolls, including Dekoni choice hybrid and Brainwavz xl velour, I felt like a
bit of the bass and treble frequencies were lost, it was noticeable enough and I didnāt like that change.
Honeycomb grills mod
I didnāt like it. You can test the how the sound changes by removing the stock grills, thatās what this mod sounds like.
I consider this a minor change in the sounds just like the pads; not worth the money and the loss of dust protection.
The good thing is the headphones feel just a bit more open and airy, giving a hint that the sound is more āclearā.
The bad: noticeable bass impact reduction, detriment to the tonal balance and rougher treble overall (in an aggressive way).
This may be good for competitive gaming (I canāt really tell) but for music it was fatiguing and less enjoyable to me than the stock sound. Itās also worth noting that the pad swaps change the sound more when combined with the honeycombs, but I couldnāt find any combination that I liked more than stock, and I tested thoroughly.