User:Kizzycocoa/tutorials/how do I add atmospheric sounds to a map
there are several answers the most common people will tell you is to put in a env_soundscape.
I personally find them very restrictive. so, I'd suggest making a normal trigger texture-covered brush, put it somewhere the player will definately pass, and make it a trigger_soundscape.
(please note, for portal maps, the portals can bypass these triggers, so I'd suggest making a big trigger brush for a whole room, or putting it next/on a portal cleanser.)
add an env_soundscape_triggerable. it doesn't matter where.
now, link the two. and fill in the soundscape info. I suggest going here, looking under "L", and selecting your game.
the soundscapes have no previews. so you shoud consider trying to make a map to test the soundscapes.
once selected, you now have a triggerable soundcape.