Speakers passed test, but this sound comes out...

[apollolux]

I have a MacBook Air, almost certainly the same speaker tech inside. Playing ultrasonic from it indeed needs output volume at a sweet spot between 25% and 40%; basically, max out your player's volume (probably iTunes or QuickTime Player) with no EQ enabled and set your system volume as close to 30% as you feel comfortable with (I have mine set to as close to 42-45% as is possible without visible numbers). If you have a means of testing output volume (apparently Frequensee Pro can do it, but the free version can't) follow what CatMan recommends in other threads.

@LeonidasXVI - she says in the OP that she has the free speaker test and used it to initially calibrate.