How far does sound travel underwater?

Factual Questions
1

I remember being in a swimming pool when younger and hearing someones watch alarm go off while I was underwater…it sounded like it was next to me, even though the guy was across the pool. How far could that sound travel?

I’ve heard about the war-games that submarines paly and a lot of it has to do with being silent. How far out can one sub hear another sub?

-Tcat

2

Hope this helps. Otherwise try a Google search using “sound travel underwater” as your search criteria.

3

Tom:

Couple of things:

Technically, sound travels an infinite distance in any material. You just need a sensitive enough detector. So, the state of the art of detecting sub noise is going to change every year as detectors get better and better.

Having said that, it’s important to keep in mind that lower frequency have less attenuation per distance than higher frequencies. (Whale songs are very low freq and can be heard for miles.) So, a good “stealth” sub will try to minimize it’s low frequency emmisions.

4

Acoustic Thermometry:

Listening to the Ocean’s Temperature
The longest soundpath in the study was 6,200 miles (10,000 km).

5

With respect to submarines, the U.S.'s new ultrapowerful sonar system is raising quite a few political hackles by supposedly causing whales a hundred miles or more away, to ground themselves. http://www.cdnn.info/article/sonar/sonar.html

6

The speed of sound in water is a function of temperature, pressure and salinity. Generally in the ocean ( the North Atlanic is what I’m familiar with ) this causes a peak in the speed of sound a few hundred meters below the surface. As the faster sound waves try to move into the slower propgating layers above and below they are refracted back to the water layer with the maximum sound propogation speed. This is what as know as the SOFAR channel and does allow things to be heard very far away.Yes thousands of miles. One can think of the SOFAR channel as the equivalent of an optical fiber for sound waves in water ( same principal ).
The government has many listening stations on the east and west coast monitoring this channel.

7

As for how far away a sub can hear another sub, supposably the new Seawolf subs are quieter than the surrounding ocean, and are nearly impossible to detect via passive sonar. Older subs, especially the Russian ones, make a lot more noise though.