Decibel levels

[Kralizec]

Originally Posted by FPSchazly

Decibel are measured differently in air vs water. To convert a water dB to air dB, you subtract approximately 62 dB. Different reference pressures are used when measuring in air vs. water. So, the 115 dB in water is approximately 53 dB in air. I think that 115 dB number is also for the submarine at "all stop" because Dot Mod reports a higher dB on the tactical map when you're cruising around at a higher speed than 'all stop'. Hope this helps.

Thanks to PineMartenEmily and tychosis for these insights.

Hey Chaz!
It's not 62dB but 26dB, so 115dB becomes 89dB when changing SPL units from water (usually 1 micropascal is 0dB) to air (usually 20 micropascal is 0dB)

There is another factor: due to the difference in acoustic impedance, most of the sound will reflect off the surface of the water, and only about -60dB makes it through.
So if you are standing 1m above a 100dB(re 1μPa) underwater sound source, due to the boundary the sound you hear will only be 40dB(re 1μPa) loud. But since in air we prefer to use 20μPa as a reference, I'll subtract 26dB -> the sound pressure is therefore 14dB