ImageTargetPlayAudio.cs

using Vuforia;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ImageTargetPlayAudio : MonoBehaviour, ITrackableEventHandler
{
	public TrackableBehaviour mTrackableBehaviour;

	void Start()
	{
		mTrackableBehaviour = GetComponent<TrackableBehaviour>();
    GetComponent<AudioSource>().enable = false;
    
		if (mTrackableBehaviour)
		{
			    mTrackableBehaviour.RegisterTrackableEventHandler(this);
		}
	}

	public void OnTrackableStateChanged(
		TrackableBehaviour.Status previousStatus,
		TrackableBehaviour.Status newStatus)
	{
		if (newStatus == TrackableBehaviour.Status.DETECTED ||
			newStatus == TrackableBehaviour.Status.TRACKED ||
			newStatus == TrackableBehaviour.Status.EXTENDED_TRACKED)
		{
			// Play audio when target is found
      GetComponent<AudioSource>().enable = true;
			GetComponent<AudioSource>().Play();
		}
		else
		{
			// Stop audio when target is lost
			GetComponent<AudioSource>().Stop();
		}
	}   
}