Why is it that some people seem to breathe loudly out of their nose constantly while others you cant hear their breathing at all.
Nasal geometry, diaphragm strength, physical activity, oxygen demand and the method used in breathing help. If you have low oxygen demands, a large nose and breath shallowly, then your breaths will be pretty quiet. But if you have high demand for oxygen, with a small nose and deep, drawn-out breaths - then it’ll be audible. That’s the principle behind airhorns - lots of air rushes past a small opening, making an earsplitting noise.