Question about 'new version' Audio Technica M50

The bass should be the same as the drivers are the same.

Here are the frequency charts:

http://graphs.headphone.com/graphCompare.php?graphType=0&graphID[]=2941&graphID[]=853

See how the M50 is barely above the HD-650 from 100Hz back?  Sure there is more bass, but not a ton.  You will probably hear more bass with the M50 due to seal and the slight +5dB bump there, but it is not going to be "oh my gosh" bass.  The ATH-M50 is a headphone I still consider to sound neutral.

The graphs aren't always a great measurement on how the sound will be perceived by the human ear.

It shows the K701/2 as having as much bass as the HD650's and M50's. Of course, the human ear won't perceive it as having nearly as much bass compared to those 2.

As for the difference in sound between older versions and newer versions of the M50, I don't think that there really is any. It's possible that some people have compared the newer version to the older version without burning them in, which is why they may seem a tad lighter on the bass when compared to an older version which has had many hours of use.

As somebody else said, the drivers are identical and should produce the same sound signature. Different ear pads may effect the sound very slightly, but I think the ear pads are also identical.

Graphs are probably a pretty decent measure of how the ear picks up the sound. Perception on the other hand happens a ways off the ear, i.e. in the brain, and is in itself unreliable (you like a pair of phones one day and on another day you'll find them boring).

Having said that, it seems to me that those particular graphs actually do show more bass for the 650 than the 701 or 702. Tyll's graphs at InnerFidelity show roughly the same amount of bass for those three models, but given that the 650 has less treble, I'd say a person would be inclined to find them the bassier headphone anyways.

Agreed the graphs tell how the measured headphone should sound.  If someone has a different experience and the graphs are reliable then the person hearing the difference either has a alternative hearing profile or is perceiving the sound signature differently.  I find that the graphs, left unbiased, are an extremely good tool for find out what the sound signature should sound like.  If I hear something different I typically start looking at my gear and player to find what is amuck.