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Old 05-10-23, 01:01 AM   #1
shake307
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Default Decibel levels

I was never a submariner. Only digitally since playing Seawolf SSN-21 in the 90s. I do know that submarines are always striving to be quiet. So, perusing the unit reference in Cold Waters, I see a Flight 1 LA Class is 115 decibels (if I recall correctly, I am at work and not playing). That is as loud as a rock concert or night club! These subs can't be that loud, can they? I get pumps are running and machinery is making noise, but damn, that seems really high. I was on an aircraft carrier and a destroyer and they weren't that loud, except during flight ops, not pier side though. Am I missing something?
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Old 05-11-23, 05:33 AM   #2
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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.
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Old 05-14-23, 02:12 AM   #3
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Well, shoot. I did not know dB levels were measured differently underwater. You taught me something, thanks.
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Old 05-15-23, 08:05 AM   #4
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Quote:
Originally Posted by shake307 View Post
Well, shoot. I did not know dB levels were measured differently underwater. You taught me something, thanks.

Glad to hear it
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Old 07-05-23, 01:14 PM   #5
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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.

Last edited by Chaussettes; 07-06-23 at 02:21 PM.
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Old 07-06-23, 07:44 AM   #6
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I often wear a fishing trawler as a hat, if I can find one headed in the right direction.

Fire a decoy to draw them, then pull right up under that noisy trawler, match its speed, and sling torpedoes with near impunity, LOL!

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Old 07-06-23, 10:37 AM   #7
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Old 07-06-23, 10:40 AM   #8
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Chausettes! nice first post!
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Old 07-15-23, 10:57 PM   #9
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Quote:
Originally Posted by Chaussettes View Post
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.

Thanks for this method as a reminder
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Old 07-24-23, 01:26 PM   #10
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Quote:
Originally Posted by FPSchazly View Post
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
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Old 07-24-23, 07:57 PM   #11
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Quote:
Originally Posted by shake307 View Post
I was never a submariner. Only digitally since playing Seawolf SSN-21 in the 90s. I do know that submarines are always striving to be quiet. So, perusing the unit reference in Cold Waters, I see a Flight 1 LA Class is 115 decibels (if I recall correctly, I am at work and not playing). That is as loud as a rock concert or night club! These subs can't be that loud, can they? I get pumps are running and machinery is making noise, but damn, that seems really high. I was on an aircraft carrier and a destroyer and they weren't that loud, except during flight ops, not pier side though. Am I missing something?
You are comparing apples and oranges, and not just because of the different micropascal references!

At the rock concert: you are in the audience and 115dB is the measured level. I'm not saying that is incorrect, that is the actual pressure that an SPL meter shows you that you hold in your hand (wear earplugs please)
But the 115dB sound pressure in the case of the LA Class is her Source level. The difference between the two numbers is the distance: source level is defined at 1m distance, and sound level drops 6dB every time the distance doubles. This is called Transmission loss.
So let's turn this into an apples vs apples comparison (or if you prefer, oranges vs oranges):
At the rock concert, let's say you are 8 meters from the loudspeaker. That means the distance from 1m doubled three times and each time the sound got 6dB weaker. We can calculate from this that the source level of the loudspeaker is 115+18=133dB
Turn this into water decibels by adding 26dB and we get 159dB(re 1μPa). Now that is a LOT louder than the 6900 ton nuclear attack submarine! Big thing designed to be quiet vs small thing designed to be loud. Isn't engineering the best?

Or compare them the other way: the propulsion and the machinery are at the stern of the LA class, and the spherical array at the bow. The distance between them is about 100m. Depending on the position along the hull where you measure, the noise level will be different: 6dB less every time the distance doubles, or generally speaking, 20×log(R). That is 40dB transmission loss just from distance, baffles come after that. So now we can compare: 115dB, minus 40, minus 26. That is 49dB(re 20μPa), which is a lot less loud than what you hear at a rock concert. It's about as loud as a comfortable conversation about submarines between friends who don't disagree which sub is best.
If you were a diver and an LA Class came up behind you, I genuinely wonder how soon you'd hear her. I don't have the faintest idea what the threshold of hearing is when one is SCUBA diving.

Last edited by Kralizec; 07-24-23 at 08:17 PM.
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