When you plug in a headphone on HTC 10 to listen to music, you can easily enable the Mono Audio instead of stereo. To switch audio from Stereo to Mono on HTC 10 when wearing headphone, do as follows:
1. Open the Settings app
2. Scroll down to the Personal settings and touch to open the Accessibility settings
3. Now, scroll all the way down to the Hearing settings
4. There you should see to options: Sound Balance and Mono Audio.
5. To enable mono audio on HTC 10, simply mark the Mono Audio option