NirCmd is a small command-line utility that allows you to do some useful tasks without displaying a user interface. By running NirCmd with simple command-line options, or via a shortcut, you can decrease or increase the system volume, mute or unmute the system volume, speak the text currently in the clipboard or text file, change the default sound device, display a list of sound devices, change the volume of an app, change the display settings, turn off the monitor, open the door of a CD-ROM drive and more…

www.nirsoft.net/utils/nircmd
Command Reference
Change Default Sound Device
List Sound Devices
Change System Volume
Change App Volume