How to Use Mono Audio on Your iPhone
If you have hearing challenges and want to use iPhone with a headset connected, you should turn on the Mono Audio feature. Using the stereo effect in headphones or a headset breaks up sounds so that you hear a portion in one ear and a portion in the other ear, to simulate the way your ears process sounds.
However, if you’re hard of hearing or deaf in one ear, you’re hearing only a portion of the sound in your hearing ear, which can be frustrating. When Mono Audio is turned on, you can set up iPhone to play all sounds in each ear.
Tap the Settings icon on the Home screen.
Tap General and then scroll down and tap Accessibility.
In the Accessibility pane, scroll down and tap the Mono Audio On/Off button to turn on the feature.
Tap and drag the slider to L for sending sound to only your left ear or R for right ear.
Tap the Home button to close Settings.
If you have hearing challenges, another good feature that iPhone provides is support for closed-captioning. In the video player, you can use the closed-captioning feature to provide onscreen text representing dialogue and actions in a movie (if it supports closed-captioning) as it plays.