[Chaussettes]

Subs are really that loud and get louder the faster you are moving, typically +1dB per knot, so a Los Angeles moving at 10 knots will be about 125dB. This is loud on it's own but a big consideration is ambient noise. You can view the current ambient noise level of the mission area on the conditions panel at the top in game. Ambient noise typically fluctuates anywhere from the mid 70s to over 120dB, and plays a big factor in being able to detect other vessels as well as the detectability of your own. For example:


A Los Angeles is moving at 10 knots and is generating ~125dB of noise. The ambient noise level is 110dB. You can get a general estimate of your real audible noise level by just subtracting the ambient noise level from your sub's noise level. So your real noise level in this scenario would be ~15dB. This would be very difficult to detect at any significant distance.


So yeah, your sub is generating over a hundred decibels of noise, but it's not really the audible noise that other vessels are able to hear, as most of it is drowned out by the ambient background noise.


A good easy to remember rule of thumb for ambient noise I use is:
70-90dB - It's very quiet, you can be heard easily.
90-110dB - It's somewhat noisy.
110-130dB - Someone is blowing into a microphone outside, it is next to impossible to hear anything or detect someone unless they are ontop of you.