You may disable in-game voice chat by modifying the built in config file.
1. Navigate to D:\Games\Steam\steamapps\common\orcs must die 2\data\startup\ and create a text file called user.cfg. Ensure that you aren't creating a file called user.cfg.txt, as this is a common mistake in this step.
2. Edit user.cfg and add "–voice." on a separate line and without the quotation marks.
Be sure the minus sign is included or this command won’t work. Use this to completely disable in-game voice chat. Disabling the in-game voice chat will allow players to use the Steam voice chat instead, should they choose to.
If you wish to modify other configuration options please read how here.