The ratio can well be 70/30 depending on your sound signature preference :D
I just got the HE-400 yesterday so it's a quick first impression with fews hours of burn-in. I did not feel the HE-400 bass was much better or prominent than that of the HE-500 (when properly driven).
What I did feel, however, is a recess in the mids, especially in the vocals range which make it sound more "heavy" . By comparison, the HE-500s do sound more open and fuller in this area. The 400s don't quite have the magic mids of the 500s.
The treble quantity is a bit more that adequate for me (I'm used to the smooth treble of the 500s), I hope it will tame up a bit with burn-in.
The interesting point, however, is that it does not require a powerfull headphone amp to show its true potential. I really (REALLY) enjoyed it on my Fostex HA-A3! The sound signature reminded me of that of the HE-500 when driven with the (slightly) warm SA-31 amp.
For $800, this is a Killer combo!
I will still give it time to burn-in and try to adjust to the change in sound signature and give a proper feedback.
Note: the pleathers were replaced with velours, of course :D. The pads that came with it are a bit flabby, more so than the pleathers that came with my HE-500...
Edited by Clemmaster - 12/12/12 at 2:02am