This may be obvious to some but it has start to stump me a bit. Let's start with some measurements (HE-6 and HE-400S comparing angled velour (green) to focus A pad (purple)). These were taken under equal volume conditions between pads (not between headphones). HE-6 HE-400S As you can see, the pads have an effect on both headphones, undoubtedly. The effect on the HE-400S is quite substantial in comparison (namely having a big difference in bass extension). Things like this have been seen before (the first thing that comes to mind is the jerg pads), where pads/mods are actually not created equal. I didn't think much about it though, at least until I saw the above measurements. blah blah blah Anyway, I'd like to start a discussion talking about the control of the planar soundwave (or the trampoline effect). At first, it seemed to me that equal dimensions and spacing (relatively) would produce equal changes in a FR, but lucky for me I have a friend who essentially slapped me in the face with the idea of diaphragm control. At this point, it would make more sense that the HE-6 is less fazed by a leaky pad than the HE-400s (dual vs. single magnet arrays). The HE-6 will quickly make a soundwave and (hopefully) not flex much when doing it. The HE-400S, however, would have less control, or at least that's how my brain logically breaks it down. The HE-400S would flex much more, like a trampoline, producing waves around in all directions as opposed to a planar wavefront. I was somewhat convinced it was as simple as that. Channel the HE-400S sound with Focus pads/electrical tape and you won't lose any bass. But then I remembered the jerg pads. Dig through some pages on changstar (HE-400 jerg and HE-500 jerg) and you'll find that the HE-500, much like the HE-6 above, doesn't care as much about the jerg pads as the HE-400 does. Okay, 500>400, so maybe, even with their dual magnet arrays, the 500 is just more controlled. Then what's up with the killer HE-400 bass distortion measurements (stock vs. stock)? It seems there is more going on here than simple driver control. There is info on this scattered around changstar but it was few and far between. And maybe distortion has nothing to do with any of this. Anyone have any ideas?