So I thought it might be an idea to make a tutorial for making efx files. Here is a draft:
Make an efx file for a mission with info_location's present.
1. In DR create a new filter: Filter > Edit Filters > Add
2. Filter info_locations:
Index 0: Type entityclass, Match .*, Action hide
Index 1: Type entityclass, Match info_location, Action show
Optionally you can add: Index 2: Type entityclass, Match worldspawn, Action show
(this roughly adds the map's layout to the 2dview, while it's still easy to see the info_locations)
3. Activate made filter
4. You see only the info_locations in the map. write down the names of all the info_locations.
5. In the fm make a folder efxs and inside that make a file "map-name.efx". So the file needs to have the same name as your map and the extension needs to be efx.
6. It's best to copy over the contents of another mission's efx file so you have the structure.
For example Requiem:
7. Here you need to change after eaxreverb "Name", which is the name of the info_location you wrote down in step 4 and after preset comes the efx-preset you think should be used for that location.
A way to easilly check the correct reverb is to start tdm inside the map/mission and use console command teleport info_location-name.
Then you can test a set reverb in the file. When you want to test another reverb, you can change it in the file and then in tdm use console command reloadsounds, so you don't have to reload the map.