There is no simple setting.
Without modifying system files, this seems to be the easiest way:
When changing the volume on a Mac, you get a big ugly gray bezel showing the change in volume. This is super annoying when (say) watching a movie. Is there any way to disable this?
apple.stackexchange.com
In automator, create a new service that takes no input. Give it a single action: Run AppleScript Enter the following AppleScript:
set x to get output volume of (get volume settings)
if x > 10 then
set volume output volume (x-10)
else
set volume output volume 0
end if
Save the service with the name "Volume down", and bind the service to F11.
Create another new service that takes no input. Give it a single action: Run AppleScript Enter the following AppleScript:
set x to get output volume of (get volume settings)
if x < 90 then
set volume output volume (x+10)
else
set volume output volume 100
end if
Save the service with the name "Volume up" and bind the service to F12.