I've put the JVC SZ-2000 "protein" earpads on the 400I. Impact greatly increased and the total sound changed for the better.

HiFiMan HE-400i vs HiFiMan Sundara 2020 Side-by-Side HiFiMan HE-400i vs HiFiMan Sundara 2020 Side-by-Side

I just applied Amir's EQ using Roon on this can. Wow, what a difference! Amir was right when he said it takes the 400i from a mid fi can to something almost approximating my HD800! However, I could tell immediately that the sound is way more cramped and not as finely detailed as my HD800, but besides that, it certainly is a great sounding can! Would my X3&E12 combo be a good enough source for the HE-400i? i am using it with the Fidelio L2 and i’ve been very pleased with the result so far, i was thinking of upgrading to the HE-400i..or the X2..HD600/H650 vs HE400i: Straight off the bat, there is no clear winner, it will ultimately be your preference that determine which headphone is right for you. The HD600 is commonly compared to the HE400i. Some reviewers say that the He400i is as neutral as the HD600, which I do not agree with because if anything, the He400i is more closely related to the HD650s in that it has that bass. Of course, both do not have a lot of bass but they have more than neutral headphones like the HD600s. He400i sounds livelier than both HD600 and HD650 but vocals come in much more euphorically in the HD650s because it is much more present due to the rolled off highs. Some may rather prefer the more natural sounding vocals and instrumentation in the He400i. Undaunted I tried my UAPP app. For those of you who have this I used in bit perfect mode and tried some radio channels as I don't have any music currently stored on my phone. The attempt through this app was far better and yielded a less thin sounding result. The bass reaches well down almost touching sub bass and it is very tight , well defined with satisfying layering but lags a little bit in body and physical presence as it is more ethereal than visceral.

HiFiMan HE-400i vs HiFiMan HE400se Side-by-Side Headphones HiFiMan HE-400i vs HiFiMan HE400se Side-by-Side Headphones

This is not the case with the current model, which despite some accentuations at the upper mid range area it sounds much more restrained and controlled without being sharp. Just FYI, I didn’t find I needed to mod the grills. My headphone didn’t actually come with padding inside so the sound was less impaired compared to some forums I had seen. I bought these second hand and I’m not sure if the previous guy took them out.The Hifiman HE400i 2020 version is fuller and more heavy sounding with more body from top to bottom. It is also more spacious and airy sounding, and has the better extension in the width as well as in note extension. The 400i 2020 compared to the se version sounds warmer, smoother. The se-version is lighter, more realistic and it sounds a lot more clear and clean. Its tuning is more neutral than that of the warmer HE400i 2020. Bass in the 400i 2020 is much bigger and the mids are weightier but you do get better extension and decay of the notes, with a wider sound stage. Treble is both headphones is easy and soft on the ears, nothing really spectacular to report here. So when it comes down to choosing as always it is a matter of budget and preferences with the cheaper HE400i 2020 version offering a more monitoring and neutral character against the most warm and full bodied Deva. The Hifiman headphone we’re looking at today is the HE-400i 2020. It’s an update of their HE-400 series headphone, but we’ll go into that in the next chapter. Upper mids are more restrained at the Deva resulting in an easier going presentation but there is a slight emphasis at about 5KHz that some people might find annoying. One thing I’m not getting is that more expensive V90 fr. range ends at 60Khz and chaper G103-S is at 150Khz. Perhaps I misunderstand real world implications of this? Is it actually unable to produce any sound freq. beyond 60Khz? Seems unreal.