Vibration effect.....make more violent?

i have text which i have created to vibrate using this code

onClipEvent (load) {
// movie width/height
height = 150;
width = 500;
this._xscale = this._yscale=temp;
// setting initiaion position
cx = this._x;
cy = this._y;
onClipEvent (enterFrame) {
// causes the object to be offset
this._x = cx+(1+Math.random()*5);
this._y = cy+(1+Math.random()*5);

i edited it from the original kirupa tutorial on circle vibration, but does anyone know how to edit that so the vibration becomes more violent over time?