If you hear a crackling sound its to loud, when I set my US on full volume of my samsung S7 I will hear the crackling sound. If I recall it right, that would degrade the ultrasonic as phones have no 20khz range.
Also, having US directly on full volume to ones ears would cause ear damage. I played US when running ASC 5g only on my computer, while calibrating the volume that I would just hear the screeching and then go just slightly under it, so I know the US was playing yet not hearing the screeching ( or just faintly ) having US to loud causes in my case headache and eardrum irritation and possible tinnitus. On headphones I only would play masked, on phone the same.
The trials you encounter will introduce you to your strengths. - epictetus
