I had a pair of HD65, but returned them.
They use FM radio broadcast technology.
They don't have to be line of sight to work.
I found them unacceptable. Even right next
to the transmitter I heard lots of noise.
Moving around that static would get worse
or better depending on where I was, and which way
my head was pointing. Sometimes I could get
a signal 100ft from base, sometimes only 20 feet.
Probably depends on building construction method
in various parts of my house.
Basically, I found the HD65 to sound like
a cheap fm radio played on an OK set of cans.
The sound was fair at best. If you can get
around the horrible S/N ratio they might
be OK. The HD85 have higher S/N ratio. I did
not listen to them because there would still be
fading problem.
The other alternative for wireless is IR.
This is line of sight - same technology used
in most remote controls. If you put your
body, or anything else between the transmitter
and receiver, you'll lose your signal. I haven't
listened to any of these. I decided I'd live with
a wire, and bought an extension so I had the range
I needed.