Play random sound

I have imported 4 songs into the Adobe Animate CC library, and I want to randomly play one of these songs via AS3.

I have given them class-names: "music_1", "music_2", "music_3" and "music_4"

I am trying something like this:

var mySound:Sound = new music_[Math.floor(Math.random() * 4 + 1)](); mySound.play();

(It gives an error: "Access of undefined property music_.")

With ActionScript 2, I could do this:

this.createEmptyMovieClip("myMC",1); mySound = new Sound(myMC); mySound.attachSound("music_" + Math.floor(Math.random() * 4 + 1)); mySound.start(0,1);

But can't figure out how to do it in ActionScript 3.