Trying to stop a sound channel from a movieclip

1

i created a sound channel that starts to play i sound when a movieclip opens:

var sound1:Sound1;
var _soundChannel2:SoundChannel;
sound1= new Sound1();
this.openPop_btn.addEventListener(MouseEvent.CLICK, pop1Handler);


function pop1Handler(event:MouseEvent):void
{
    event.target.alpha = 0;
    TweenIn = new Tween(popUP1_mc,"alpha",None.easeNone,0,1,1,true);
    _soundChannel2 = sound1.play();
    }

this code fades in a movieclip named ‘popUp1_mc’. inside this Clip i have a close button that closes the clip:

function closeWindow(event:MouseEvent):void
{
    
    MovieClip(this.parent).openPop_btn.alpha = 1;
    MovieClip(this.parent).popUP1_mc.alpha = 0;
_soundChannel2 = sound1.play();
}

this:_soundChannel2 = sound1.play(); is a mistake ! how do i connect with the sound
from inside the Clip??
:*(