So while the Voodoo Cursed Souls do not change your voice to low by default, a Halloween Spell such as the one listed above can modify the cosmetic so that it does lower your voice (on Halloween servers). Halloween Spell: Sniper's Deep Downunder Drawl.Halloween Spell: Medic's Blood-curdling Bellow.Halloween Spell: Engineer's Gravelly Growl.Halloween Spell: Heavy's Bottomless Bass.Halloween Spell: Demoman's Cadaverous Croak.Halloween Spell: Soldier's Booming Bark.Halloween Spell: Scout's Spectral Snarl Putrescent Pigmentation Sinister Staining Chromatic Corruption Exorcism Spectral Flame Gourd Grenades Voices From Below.These spells are unobtainable for now (only during Halloween) but you can purchase items that have those effects on the market still. The 1 all class spell isn't a standalone spell, but the byproduct when a class specific spell is applied to an all class cosmetic. There are 9 class specific spells that alter your voice, one for each class, and 1 all class spell (Voices from Below). A wiki article is here if you'd like to read more, but I'll sum it up for you. Those Voice Modifications are from the Halloween Spells in TF2.

Voices from below tf2