In your search results, if you click onto one of the files that show up: you'll see a window to the left of the results that is titled media. It groups the media according to video, audio, etc. So if you click onto one of the types of media (icons), only that type of media will show in the results. To show all again, click (All) at the top of the group. Or in your case press audio so it only shows audio files in the results.