Hi everybody, I got a last question and after I will not annoy you any more. 
I just want to know if it is possible to not let a sound cross a wall ? For example I have a little music loop in a room, but we can hear it outside, it’s not realistic.
Thanks a lot !
AFAIK you can’t block a sound. Maybe it helps if you place multiple target_speakers with a low volume into the room? I’ve never did it myself and don’t know how the sound is distributed.
Multiple identical looping sounds will just increase volume without any speed cost.
Sound should be blocked by an efficient PVS… So, if you run around with showtris 2 and you cannot see the triangles inside the room, your sound should be blocked, too. If you can see the triangles inside the room, go and read something about vis blocking.
it can be done with this: http://simland.planetquake.gamespy.com/ldr1_1/speakereditor.htm
mess around with the settings and you will get it:)
A normal target_speaker is not broadcasted outside the visible portals unless global or no_pvs is set on the spawnflag so you really do not need to use the speaker editor for it. But as CooperHawkes said, if the engine can see the room it will not block the sound.