Supermutants in Fallout 3 have a distinctly(Imo terrible) voice. very high uneven pitch and lots of voice cracks. They really don't sound like 10 foot tall ubermensch. They just sound..well... "Special"..   
With this mod I've made all mutant voices deeper, whilst trying not to go overboard into cookie monster territory.   
Now, every mutant from Fawkes, to Uncle Leo, to the random Mutants bantering with each other will sound like the hulking monsters they are, and not disabled teenagers in the midst of puberty.(Okay that last part is a bit facetious, but still, they sound bad, download the mod, make them sound good.)

Feel free to offer suggestions, for example: If you think the voices aren't deep enough, etc.    

Inspiration: Inspired by the "Deeper voices for Mutants and Strong" from the Fallout 4 Nexus

Installation: To install merely extract the contents into your data folder of use NMM, vortex, etc.  
If you're using any of those then you likely already have archive invalidated, so it should work from there.  :D
Enjoy the scarier sounding mutants.

New Vegas Version:
https://www.nexusmods.com/newvegas/mods/67722?tab=posts

Highly recommended mods: 

Deadly Creatures- Fallout 3:  
https://www.nexusmods.com/fallout3/mods/23787
(Makes Mutants into formidable opponents instead of pushovers, giving you more time to actually hear their voice lines in combat) 

Fallout 3 Hirezd:
https://www.nexusmods.com/fallout3/mods/19931?tab=posts  
The undisputed best Fallout 3 Supermutant retextures(Disclaimer: Opinion... But still, undisputed.) Gives the mutants a more aggressive and monstrous appearance to match their new voice