What amp are you using?
Joutenheim w/balanced dac primarily. The 400i sound excellent with EQ. I use True-Fi by Soundworks.
Hmm, I wonder if your opinion would change on a different amp
Also sonarworks is pretty great
If you look at their frequency response the 400i have a sharp roll-off under 100HZ. It’s not a big deal really, I use EQ with every headphones I own. They all have too much bass roll-off, mid-bass hump, treble peak, etc. I just bought an iFi Zen Audio amp/dac, but I haven’t tried the 400is on it yet. For me, Sennhesiers are the only ones I could listen to without EQ if I had to.
The 400i is fairly linear down to 40ish imo and starts to noticeably roll off. Do you wear glasses?
Nope. I am going off the graphs on Soundworks. It’s easy to hear. When I say that they have zero bass, I mean it. With EQ (flat line) they sound good. Perhaps I own a weird pair, which is definitely possible with HiFiMans quality control issues. I also own a pair of Edition S. I doubt that I will ever buy another pair of HiFiMans.
You are comparing a compensated target made by sonarworks, so in that case they would have that roll off you describe if you are only looking at the sonarworks target. No problems, but when you are used to the sonarworks profile you may find them lacking without
I thought the HE400i rolled off also with the all velour focus pads. With the hybrid focus pads, they rolled off, but much less so. Either way, I thought that regardless of FR, the bass sounded anemic. The 7Khz treble peak also bothered me A LOT.
I am mainly going off of the focuspads not the focuspads a here. I can see how the bass can be anemic for some, but I don’t really think it rolls off, it’s just not as elevated as some like it, which is not an issue as that’s just more preference
THEY HAVE ZERO BASS! I don’t need to look at a graph to hear it. They have less bass than the AKG K240s. They are completely unlistenable without EQ.
I owned them for over a year before I bought the Sonarworks. FYI, I haven’t changed the pads.
Perhaps you did get a messed up set then 
I’ve heard many more headphones with less bass than the 400i
I have always wondered that because others have commented on their decent bass.
I have always been lucky with hifiman somehow (a bit too trusting I might say lol). The only thing that’s happened so far with one pair has been a snapped headband on a he560v1, but otherwise no issues
Haha. I haven’t had any issues with mine, I just prefer the Sennheiser house sound to the brighter HiFimans, Beyerdynamics, Grado, etc. I just bought a pair of 660s and I love them.
Gotcha, that makes sense 
I am just all across the board for what I like lol
I need to try some more planars for sure. I almost bought the new Aeon X, but decided to pull the trigger on the 660s instead.
From what you describe you like, you may actually want to look into the lcd1, might be up your alley. Also I think the 660 most likely is more suiting your preference compared to the open x
I plan on buying a pair of LCD-1s eventually too.