Referencing files in JavaScript in WordPress Plugin

Use wp_localize_script.

function pr_add_link_sound () {

//Register the script first
wp_register_script('add_sound', plugins_url( 'add_sound.js', __FILE__ ), array('jquery'), '', true);

//Localize the sound file url to use in the script
$args = array(
    'sound1' => plugins_url( 'sound.mp3', __FILE__ ),
);
wp_localize_script( 'add_sound', 'PRSound', $args );

//Enqueue the script
wp_enqueue_script('add_sound');

}  

You can reference the sound in the js file like this..

(function($){
  var sound = new Audio( PRSound.sound1 );
  $('a').on('click', function(){
    sound.play();
  });
})(jQuery);