I have just tried it out in the custom game.
The volume of my setting before this game was untouched, so it was at 100 for Master Volume and Sound FX Volume at 100 while others were at 50%.
But after I changed my setting, the volume of the announcer and the voices of champions did not change at all.
I will be re-doing the test again.
Updating this report after the new test.
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