How to stop sound output switching to a monitor when it gets plugged in?

Solution 1:

I have multiple devices I connect to my mac and for some they had the same issue.

The work around (or actual fix) is to open 'Audio MIDI setup' in your Applications>Utility and:

• Click + in the lower left corner.
• Click Create Aggregate Device
• Turn off/on the inputs/outputs sound based on needs.

Solution 2:

I made an app for this. It allows you to pin input/output so it cannot be changed for every particular set of connected devices.

Solution 3:

You just need to specify a preferred audio device once and the Mac system will remember your choice and won't switch the next time.

1. Open System Preferences -> Sound.
2. Opt-in "Show Volume in menu bar", you will see a sound icon on the status bar.
3. Connect to your monitor if not.
4. Click on the icon and choose a preferred output device.
5. Disconnect monitor and retry, you will see the system remembered your choice.