Load soundfile into fla using only AS

I want to load a soundfile (wav or mp3) into my application. The soundfile are set in the xml file, so what i need is some code to load this and play it.

Here is what i do, which does not work:
speaker.stop();
mysound = new Sound();

mysound.onSoundComplete = function() {
speaker.stop();
};

mysound.loadSound("/welcome.wav", false);

mysound.onLoad = function() {
mysound.start();
speaker.play();
};

What is wrong here? Any ideas?