1) Start Arma 3 in Default Speakers of computer or any sound device
2) Plug in another source of sound device which is set as default device when inserted
3) Check the Arma 3 Sound source, it will be still playing in Old Default Device.
or
1) Insert Headphones and start Arma 3.
2) Sound goes to Headphomes.
3) Remove Headphones and insert again. No Sound in the game.