white noise

First things first - I don't have a frequency test mic/software, so I'm just using a mobile app to analyze the SPL in my room. Goal is to generally balance my subwoofer output level with the levels from my speakers in a way that is objectively more meaningful than "it sounds good". Audio flow...

I recently got a Truthear x Crinacle Zero, and the sound seemed too low. So I got the apple type c to 3.5mm dongle and connected it to my USB-3.1 port via the type c to USB-A converter. The sound volume problem has been resolved, but I can hear a background white noise, which is not much but...

So this one might get me the stupid question of the week award or something... but anyway: We all know hearing threshold curves, which are taken using narrow bandwidth tones AFAIK. What do they mean for minimum detectable white noise level though? How low typically is it? Are there any studies...