Here's some information that might be useful to other Sennheiser HD-518 owners.
Sennheiser is now selling a replacement cable for the HD-518 that is 4.5 feet
long with a 3.5mm plug instead of the 1/4" plug that comes from the factory.
The Sennheiser item number is 5X8SHORTCABLE. The item description is:
"4.5FT Adapter Cable 3.5 to 2.5mm for HD5x8"
I ordered mine from Sennheiser two weeks ago and received it last week.
Cost was $12.95 + $6.50 shipping.
As far as I know the only way to order it at this time is direct from Sennheiser over the phone.
I ordered mine by calling 877-736-6434. Press 1 to get to Sales.
I bought my HD-518 after Christmas to use with my HTC Rezound Android phone at work. I'm not an audiophile but I have to say that the HD-518 and short cable work great together (and sound great)!