Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Won't stay on head.

I've had luck with other Sennheiser headphones (in particular, I love the wired HD 555 headphones), but these wireless ones are just awful.There is a hiss on all channels, even at close range, and in a home with no other interference.Worse, though, is the fact that they won't stay on my head! The flat ear pieces lay flat, rather than hooking around the ears, so they just slide off your ears when you tilt your head forward or back. And the bar that rests on the top of your head is horrible also... even on it's tightest setting it is loose on a medium-sized head, and the padding provides no friction. These headphones really want to slide off my head. Definitely returning them.