3D Positional Audio is sound that comes from a specific position in-game. It's very useful for adding immersion to missions as it can be used for background ambience as well as general sound effects.
While getting a positional sound to play once is relatively easy to figure out, getting it to loop is another story. Due to the amount of outdated/incomplete information regarding this particular problem, I thought, since I finally figured this out, that I would write a guide...

So, here's the simplest way I've found to create looped 3D positional audio in Arma 3.
I'll explain how to have the audio running constantly from mission start and also how to trigger it with an event.

You'll need:

• An audio file converted to .ogg format
  
• A description.ext file in your mission folder (I'll explain how to make one in the following steps)

First, you need an .ogg format audio file to play.
(There are many free online converters or you can use Audacity to convert an mp3)

Once you have your .ogg audio file you need to place it in your mission folder.
(...\Documents\Arma 3 (Other Profiles)\--Username--\missions\--MissionName--\)

To keep things tidier, consider making a "sounds" folder in your mission folder to store all the mission's audio files.
(For the purpose of this guide, we will assume you made a sounds folder and placed the audio file inside.)

Now, you need a description.ext file in your mission folder to give your audio file a variable name.

1 - Navigate to your mission folder.
(...\Documents\Arma 3 (Other Profiles)\--Username--\missions\--MissionName--\)

2 - Create a new text document.

3 - Paste the following code in the text document:

4 - Adjust the audio file path in the code to match the path to your audio file.

5 - Save the text document as description.ext
(You will be asked if you are sure you want to change the file format. Click yes.)

Finally, you need to set up an object or trigger to play the sound in the Arma editor.
First I'll explain how to do it with an object.

1 - Place an object on the map.

2 - Double click the object and insert the following code in the object's init field:
(Notice in quotes the sound classname "sound01", which we defined in the description.ext file. If you named your sound classname something different, it needs to reflect that here also.)

3 - Notice the section of code that says sleep 150? The 150 is the length in seconds of my audio file which is 2 minutes and 30 seconds long. (2x60+30=150) Adjust this to whatever the length of your audio file is.

Sleep is the function that makes the game wait before starting the audio track again, so if you set it correctly, you will get a continuous audio loop



That's it! Preview your mission and you will have a continuous audio loop originating from the position of the object you placed.
Read on to learn how to implement this code in a trigger rather than an object.

To use this method via a trigger, follow these steps:

1 - Place a trigger on the map.

2 - Double click the trigger and insert the following code in the trigger's onActivation field:
(Again, the sound classname "sound01", needs to be the same as what you defined in the description.ext file. Also, notice that nul = [this] has changed to nul = [thisTrigger])

3 - Adjust the sleep length to match the length of your audio file in seconds.

4 - Now you can set the trigger's conditions. Fulfilling them will trigger the audio loop with the sound originating from the trigger's position.