A:Answer Depends if you are connecting to computer or TV. These easily connect to desktop or Laptop computer with the supplied adapter. They also connect to TVs with an audio out plugs. Unfortunately not all TVs have two speaker out plugs, one that shuts off the TV speakers, and one that lets the TV speakers run at remote volume, and a different headphone volume. You will find that many TVs have one audio out that kills the TV speakers, and a digital out that requires a converter to play TV speakers and Headphones.
The Sennheiser RS 175, RS 185 and RS 195 Wireless Headphones have the ability to connect directly to a digital optical output that is outputting a PCM signal (most TV will sense this or provide a setting with the remote).
Orei DA34 Digital to Analog Audio Decoder is what Sennheiser suggests.
https://en-ca.sennheiser.com/what-headphones-can-connect-directly-into-a-optical-audio-output
JR