If the 8400's bass is farty, I would hate to see your impression of the bass on the XB500!
Maybe you have a lot more clamping force than I do.
I always see these listed as an alternative for those that like the M50 and I'm all confused...
BTW what has neutral bass to you?
I think I'd consider the bass of the Beyerdynamic DT250 250Ohm or of the AKG K550 to be neutral. M50 is a bit bass-heavy.
With the 8400, I literally meant that the bass sounds like someone farting. I think that volume-wise, the bass is actually pretty neutral on the 8400, although the upper bass does get lost beneath lower mids on occasion (particularly in heavy rock songs where rhythm guitars often drown out the bass on these headphones). So yeah, it is not that the bass is too loud or too muddy, but it does seem to lack something, perhaps it is what people call 'impact' on these forums. What I mean is that you hear the vibration of the bass instrument (ie. fart) but there is no physical impactful element to this bass, which would usually 'fill in' the actual sound of the instrument and make it sound more like a note is being played rather than just the texture of the note. Instead, what I get from the 8400 is just that vibration bit, which sounds like someone farting.