Spotlight not indexing /library/audio

Spotlight does not search system folders by default.

In a Finder Search, you can add System Files to the list of criteria which should allow you to search that folder.

In the criteria popup menu there is an Other... item. Select it, then scroll down and add the System Files to the menu by checking the box. You might want to add File visibility while you are at it.

Now, you can add System Files Are Inclueded in the search.

Or do I have to select this specific criteria every time I want to search in systems folders?

Yes.

You could create a Saved Search with that criteria. Then, when you open the Saved search, you just type in your search term.

It won't show the Criteria, but they are there. If you right-click in the window, you can select Show Search Criteria.

An alternative for searching for file names is Find Any File. It searches were Spotlight can't: invisible files, system folders and inside packages. Although slower if the file is on the HD FAF will find it.

OT