^I can mod it for him using the same method I modded the HD600. I think the HD650 will respond better since it has lower bass distortion to begin with, and a more reasonable EQ. HD600 is slightly V-shaped at stock.
Have you guys ever tried open cell foam? You can basically get it at your local Walmart for 50 cents a bag. I used it before to dampen midrange reflections on pair of technics sb7000a I use to own and it worked well. Used it for my 240dfs before with good result as well before they bit the dust by testing an old guitar amp cause it sent DC through the headphone jack...anyhoo, I'm just guessing it can work pretty well for the back screening of the hd600/650 maybe..
The closest Walmart is about 1 hour from me.
But I'm open to everything, so... will try to get some and will report back. I should post a HD600 modding guide on the new site, too. The mod has been finished for a long while already, but I need some trusted ears to confirm that the mod does make sense.