public class ControllerHaptics : MonoBehaviour {

     SteamVR_TrackedObject trackedObject;
     SteamVR_Controller.Device device;

     GameObject[] soundSpheres;

     // Use this for initialization
     void Start()
     {
         trackedObject = GetComponent<SteamVR_TrackedObject>();
         device = SteamVR_Controller.Input((int)trackedObject.index);

         soundSpheres = GameObject.FindGameObjectsWithTag("Grabbable");
     }

     //Update is called once per frame
     void Update()
     {
         FireHapticsBasedOnDistance();
     }

     private void FireHapticsBasedOnDistance()
     {
         foreach (GameObject soundSp in soundSpheres)
         {
             // controller approaches Sound Sphere
             if ((transform.position - soundSp.transform.position).magnitude < 0.5f) //if the distance between the controller and the Sound Sphere is less than 0.5 then:
             {
                 //we have found a Sound Sphere close to a controller
                 device.TriggerHapticPulse(600); // <------- this value should increase as the above magnitude decreases. note that this value is a "ushort" value and probably needs to be converted?

                 break;
             }
         }
     }