Problem with streaming audio and play in trigger area

When I step inside the trigger area, "PositionTrigger.room_a" will return a String like "101",then it's checked if true, the audio will play, but nothing happen. But when I come out, the audio plays. Here is my code.

public class AudioRoom : MonoBehaviour {

 public string audio_room = "http://..../101.ogg";
 void Awake()
 {
     
     WWW www = new WWW(audio_room);
     audio.clip = www.GetAudioClip(false,true);    
     
 }
 void Start () {
     
 }
 // Update is called once per frame
 void Update () {
     
     if(audio_room == "http://.../" + PositionTrigger.room_a + ".ogg")
         {
             Debug.Log(PositionTrigger.room_a);
             audio.Play();    
         
         }
         else
         {
             
             Debug.Log("Blank");    
         }
     
 }

}