Thats too quiet. Adjust to max -20db like in the article described.
If after a while you get a headache or tinnitus, just turn down the volume until you feel comfortable.
I had the volume always -30db on a galaxy s9 cell phone two meters from my head. You have to experiment a little.
I still donāt get it thenā¦ if I play music at 50% its too loud and I thought the literature reg ultrasonic said its really loud?
did you try to use the internal speakers of your iphone and take a measurement with frequensee?
no it was too quiet. my fault.
Could be also a problemā¦