Tournaments are only over once all players bust out or only one player remains. To "manually" force this you can either bust players out or perform a chop (Ctrl+C or press the Chop button on the Controls tab). Since this will end the tournament, you can trigger a sound by using the "the tournament ends" trigger on an event. I don't think there's a way to differentiate between a chop ending the tournament and a final bust-out ending the tournament.