Originally Posted by MrMateoHead
Actually the response plots (not the waterfalls) DO look rather similar at a glance. What is more obvious with the HE-400s is the 1 Khz 'hill'. The 400s appear to take about a 10 db 'scoop' out of the 1-6 khz area while the 500's do about 5 db. I assume this makes the HE's appear to have a more 'recessed' upper midrange than the 500s, but the response is overall less flat. That and it probably tames the bass quite a bit.
It is more difficult to see that, in treble extremes, the HE-500 actually do inherently what many do when they EQ the HE-400, which is kill response in the 10-15/20 khz area. Other than that, it is obvious that the HE-500 has different square wave response and lower distortion. Wish I could hear the 500s for a more precise sense of what is going on with them. They are probably quite close to what I try to make the 400s sound like at times.
The thing that hurts HE400's treble so much, and that is the major difference if you A/B between the innerfidelity measurements of 400 vs 500, is the extra peak in the 400 response centered in the teen kHz's.
That is not a benign peak either, as the CSDs do indicate some minor ringing trailing from it (which could explain why the "tizz" is still there, albeit in less amount, when HE400 owners do everything from using pleathers which tone down treble, and straight EQing which also does it - if there is ringing, the tizz sticks around).
This is unlike HE500's treble hump which is just a clean hump that decays fast like the rest of the spectrum, and which reacts remarkably well to any kind of attenuation, whether it be pad change or EQing. It's like playdo.