Since i was not able to figure out how to make it work,have chosen other solution which is much simpler so that in case somebody need it can refer:
Place this above end of body tag in master page:
<audio id="audiotag1" src="sounds/sound.wav" preload="auto"></audio><script type="text/javascript"> function alert_sound() { document.getElementById('audiotag1').play(); } </script>
and now you can call it any page on page load:
ScriptManager.RegisterStartupScript(this, GetType(), "PlaySound", "setTimeout(function(){alert_sound();},10);", true);
Thanks!