You mean the so-called talkie version of FOA, it's a special "enhanced CD-ROM edition" which was released in 1993.
I assume you've got the normal version of 1992 which only has MIDI music and text dialogues (if there ain't a 150MB file named 'monster.sou' you don't have the talkie version).
If you are an US resident you can still purchase it at Lucasarts' on-line store. Here in Europe it is not available anymore.
Took me half a year to find the talkie version at eBay, payed more than $200 for it, but now I'm a proud owner. Sorry, won't sell it ;-)