This document shows how to force all audio to a single channel
To find this option, click the Start button and select the gear-shaped “Settings” icon.
Click the “Ease of Access” icon in the Settings window.
Click “Other options” in the sidebar. Scroll down to the bottom of the window you’ll find “Mono audio” under Audio options. Set it to “On”.
That’s it! If you ever want to disable this option and re-enable standard stereo audio, just return here and set Mono audio to “Off”.