I made these measurements (FR and waterfall) some time ago.

http://diyaudioheaven.wordpress.com/headphones/measurements/brands-s-se/

Added some info about old and new pads as well.
HD650 is somewhere in the middle of the page.

I use it with stock foam in front and back.
Sennheiser didn't just wing it and the foam appears to be there for a reason.

Time for my HD650 measurements. Stock for stock, I like these more than the HD600, mostly due to the smoother 1-4KHz response. I did prefer the treble rendition on the HD600 otherwise. I wish they would make a baby. The more laid back upper-mids and treble on the HD650 make the mid-bass hump stand out more, so they sound thicker and woolier. On the upside, the HD650 does have improved THD results. CSDs look clean as always. That stuff below 1-2KHz or so is just inherent to my setup - not gonna get much cleaner from a headphone (my lookback measurements show resonance crap there too for whatever reason). Overall, not bad looking at all. Why would you buy the PM-1 again? (Again, PM-1 will work OK from about anything. HD650 probably won't. But other than that...)

Like on the HD600, I think the raw 1 and 2 measurements match what I hear a bit better than the 3rd and 4th takes. I don't think they sound as dark or veiled as measurements suggest, but they are on the laid-back side for sure.

Oh, and these were stretched out over a bookshelf speaker for a couple days, so the pads are a bit softer and the clamp isn't quite as tight as fresh out of the box.

The pattern reminds me of the Orpheus FR lol.

http://www.changstar.com/index.php/topic,382.0.html

Some measurements I'd like to share for dt990 pro(relatively new pads), hd650 and hd595(moderately worn pads), using a radio shack spl meter, a CD on top of the former's mic and "room equalization wizard"(REW).

I did this more so as an experiment trying to capture the relative differences, on the ground that the process is the same for the three sets. I don't know if I'm scientifically correct regarding my goals(if not please explain-ok sound levels are not matched exactly but this is not of paramount importance). I performed three measurements for each set with repositioning just to be sure about the consistency of the results. The above graph shows the best case scenario as there were no significant diffenences except for the bass levels. as you can see data are raw.

At first I was puzzled when I saw how smooth 650's FR is, until I measured the others. These results are in line with personalaudio.ru tests with the exception of the uppermids 6db notch. I wonder how marvin's upper-mids "marianna trench" came out. To be honest Marvin I haven't found any post in here explaining the whole procedure in detail.

As you can see H595 has serious bass roll-off(some of it is due to the spl meter I think) and sound tinny, although flat. On the other hand 990pros suffer from a midrange dip and a very deep notch around 4K. I always considered dt series as lacking in the mids(excessive dullness and distant feeling) and now I think I found the true cause. Again, many internet measurements prove to be perceptually deceiving.
HD 650 sound to me more or less as I measured them. Flat, true to the source, vivid in the mids with somewhat weak extremes. As I have auditioned Audeze LCD-3 recently the most important improvement I recall over the 650's is in the bass sector(extension, clarity, smootheness). Mids just were just different(less pronounced/shouty), not better.

Ok but ratshack remains the same for every set you put on.
To clarify things, I didn't use an ear dummy. That's the main reason you will never see results such as those on serious sites like e.g. innerfidelity. My purpose is to capture relative differences.
Also, i'd like to mention that if I correct my dt990 pros according to marvin's measurements, or even other more "professional" ones, the sound becomes worse than 20 USD sets sometimes. I'm sure you have noticed the ridiculous differences among the so called serious tests.