How to fix a "X3DAudio1_7.dll is missing" error
See if updating Direct X helps -
[ EDIT: Updated link 25 June '16 ]
If you get a message that your Direct X is up to date the problem may be due to a corrupt DX file.
You could locate the x3DAudio1_7.dll file in System32 and delete that file.
Run the Web Installer again to replace it.
Or - Reinstall Direct X using the full Direct X installer package. This will overwrite all DirectX files. -