OK, to address all your requests for comparative plots for the 840 and Dog Pad, here are charts are from a typical unit that went through an upgrade from 840 to Dog Pad... These charts are the same headphone before and after.
The purple is the 840, the red is the Dog Pad. You'll immediately see two key differences, below 200 Hz the Dog Pad is much flatter, and has better sub-bass extension. Because there is less of a "bump" from 80-200Hz, the low bass actaully sounds more prominent and balanced. Also, as the peak at 1K is smoothed out, so there is a little smoother sound to the mids, they feel more natural and balanced, with less of a dry overtone and a more lush overall presentation.
EDIT: If you are not familiar with headphone frequency response curves, don't be alarmed by the large rolloff over 1K and the "peak" at 7-10K, headphone meaurements are VERY different from loudspeakers. See Tyll's excellent writeup on InnerFidelity
here for more info.
In the time-domain, here is the original unit with 840 pads...
Decay is very smooth with only minor bumps below 1000Hz, and no resonance modes (which show as large ridges) anywhere in the spectrum.
Now here's the same phone with the Dog Pad:
You can see that the area below 1000Hz decays even faster, as does the ENTIRE spectrum (note how there is almost no yellow, this means the sound energy has decayed much faster than with the 840 pads, and the 840 version was already very fast). This gives the phone a greater sense of dark space and better separation.