I've never gotten the windows voice ducking to work with TeamSpeak 3 on Windows 7. I haven't tried with Windows 10 yet. I use a TeamSpeak 3 Plugin called Volume Control which you can get here: http://addons.teamspeak.com/director...y)-remake.html
It says Windows 7 only - but it works with Windows 10 as well (I'm using it).
Description for the Plugin: This plugin lowers volume of all other applications when someone talks.
You can also change it to whatever amount you want it to lower all other applications by.
Click on the windows loudspeaker once with your left mouse button.
Click on the pop-up "Mixer" and equalize all programmes to the same level if they aren't.
Note this only shows active programmes so make sure that all the programmes are active you are dealing with.