Change Audio preferences for accessibility on Mac
On your Mac, use the Audio pane of Accessibility preferences to make the screen flash when an alert occurs and play stereo sound as mono.
To change these preferences, choose Apple menu > System Preferences, click Accessibility, then click Audio.
Flash the screen when an alert sound occurs
Make your screen flash when you receive an alert.
Test Screen Flash
Demonstrate a screen flash.
Play stereo audio as mono
Make your Mac play stereo audio tracks as mono audio in the left and right speakers or headphones.