hearphone and ultrasonic silent

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I listen to ultrasonics with headphones on my iPhone at 50% volume and I've volume locked my iPhone so I know it will never go higher. I can hear ultrasonic frequencies so I'm comfortable with where it's at. Most of the time it's low enough that I can't hear the ultrasonics anymore over the train/street noise. Also no tinnitus. I get more tinnitus scares listening to ultrasonics at night where I've calibrated it to ~28db.