Adding new sounds to System Pref "sound effects".

[dgurney]

Because you are doing the procedure wrong. What's the name of the sound effect program you are trying to use?

What "procedure"? The guy's not doing a procedure. He asked how to add sound effects to his Mac. He's not using a sound-effects program; he clearly said he downloaded some sound files.

The Apple article says you need to convert the files to AIFF and put them under

/Users/(your user ID)/Library/Sounds

Under Lion, Apple has ignorantly decided to hide the Library directory, so first of all you need to make it visible again by launching Terminal and then entering

chflags nohidden /Users/[username]/Library

Then you can drag AIFF files into Library/Sounds and they're supposed to show up in System Preferences.

You could probably also go to the system-wide Library directory, add a Sounds directory under it, and put AIFFs in there. These would be visible to all user accounts on the system, not just yours.

[jbarley]

I think after 4 years the OP either has the problem solved or has given up and moved on.