I appreciate you don't wish to use any third party software, but as an option for si vous ne mind using a 100kb exe, vous pouvez utiliser Nircmd with the commands:
nircmd setdefaultsounddevice "Speakers" 1
or
nircmd setdefaultsounddevice "Headphones" 1
Vous devez assurez-vous you use the exact name of your audio devices as listed under Playback Devices (clic droit the sound control in the zone de notification). It may be easier to rename them under Properties to simpler names, especially if the names clash in any way.
The 1 at the end of the command signifies "Default Device". Using 2 signifies "Default Communications Device".
If you really don't want to use a third party tool, here's a diff of a registry key that seems to change when I change my default sound device, it may be of some use to you, but Je ne sais pas exactly what it's doing. It's not as simple as a 1 or a 0 to indicate if it's a default, it would seem.
