I found a fix for my problem which also aapplied to DayZ standalone. All you have to is right click the ArmA 3 exe file and click troubleshoot compatability. It will the run the game with sound somehow. The next time you run ArmA 3 you can run it normally without having to right click and hit troubleshoot compatibility.

Sadly no. It happens with whatever sound output I'm using. If I use my headset: nothing. If I use my speakers: nothing.

I'm having the same issue. Just randomly out of the blue ArmA 3 sounds just stopped working. I used to not be able to see it in the volume mixer but now it's appearing but still no sound. I've tried everything as well (DirectX, windows hotfix, changing playback settings, volume control options, in-game menus). This also only happens for ArmA 3. Not any other game I own. I recently checked the rpt files located in the appdata/local/arma3 folder and it says this:

23:42:47 Sound engine not initialized properly - dummy sound implementation used, NO SOUND !!!
23:42:47 InitSound ...
23:42:47 InitSound - complete

What does this mean? It looks like I've found the problem but I've looked everywhere and I can't seem to find anything related to fix it. Help please. Thanks.