my headphones are stereo but I would like the sound from the left and right to be combined then sent to both headphones.
The reason is I'm watching a video where the people speaking are in the right ear as well as the music but they never speak in the left ear (it is not because they on the right side of the screen) If I take the right headphone off then I only hear the music in my left and there is no speaking.
Control Panel > Sounds and Audio Devices > Audio > Sound Playback > Advanced
? You can set the speakers & headphones to all possible "Mono" choices you might have.