You can use the MediaElement.Balance property. Setting it to -1
will have 100% of the volume go to the left speaker and 1
will move the volume to the right. 0
is center so the volume is evenly distributed to both speakers (this is the default).
Let's say you want to move all the sound to the left speaker, you can set it in XAML like this
<MediaElement x:Name="MySound" Balance="-1" Source="/sound/haha.mp3" Visibility="Collapsed" ></MediaElement>
Or from the code behind like this
MySound.Balance = -1.0;