How do I get sound working in Luigi's Mansion of the Dolphin Emulator?

I downloaded Luigi's Mansion to play it on my computer and the game runs and when it starts it shows the Nintendo logo and it says "Nintendo" in that spooky voice, so you would think it has sound but after it says Nintendo there's no more sound. And before you guys freak out and say its Illegal to download games. i already have a copy it just doesn't work anymore