If you have a copy of the manual - then have a look through the list of commands. You should see one which says or relates to 3D sound usage - The manual explains briefly the command and what it does.
So as to make things simple - find a default FPSC script for an entity that uses a sound and copy it somewhere using a new name like - soundtest (best use an entity script which is not from a character) - open it in Notepad and find the line of script which tells the entity to play its sound. Simply update with the indicated command from the manual for making a sound 3D.
You can also use the volume, range and loop functions for instance to play ambient sounds and alike in specific locations that will of course fade in and out depending upon player proximity.
You can use a simple box entity for this, making it invisible and passable and place it in your chosen location attaching your 3D sound script to it - you wont need use a sound zone marker that way.
