![:glad:](http://192.241.182.11/images/smilies/glad.png)
I've recently figured out how to do this, make a soundscapes.txt file in for example-steamapps/(steam account name)/half-life 2/scripts folder. If there is not a scripts folder, make one. In the soundscapes.txt file write a code such as-
"echo"
{
"dsp" "28"
}
The dsp is a sort of sound effect command, and the number selects what sound effect you want,like dsp 20 is loud echo and dsp 23 is very long echo. Now make a map and a simple hollow block, info_player_start, and an env_soundscape entity. Type in the soundscape as echo. Now compile and run the map. Shoot a weapon andthere should be an echo sound of some sort. Happy modding :D.
Note-the dsp number 29 may vary with other source games, so far it works for half life: source. Just try out other numbers (such as 1-50) and see if there is any effects. If I find a HL2 dsp effect I'll post it.