You can tell these hardy Sennheiser veterans mean business. Metal construction gives a vice-like fit on your dome and speaks of their ineffably high-end sonics. You'll need an adaptor to plug them into an iPod; these are built to be part of a nice little home hi-fi set-up.
Sound is flat-out the best here; Across a full gamut of musical styles the HD 650s serve up smooth, subtly conveyed sound, but when you want them to kick out the jams, these metal mothers don some large-style boots.
The open-backed design leaks sound like a sonic sieve, so these are totally unsuitable for wearing on the tube, unless you enjoy "chin music" courtesy of your fellow passengers; Given that they're thus intended for long, immersive home-listening sessions they could also be more comfortable.