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Dear Pierre.
As a diver I can give you my take on
underwater sound. There are dive sites online you can go to for more
information
but although I have read some of them I do not know
their links offhand. You would have to search underwater sound or underwater
communications.
Water is 800 times more dense than air. Sound also
travels faster thru water than it does thru air. However, underwater it is very
difficult to
determine what direction the sound is coming from
or to understand what exactly that sound is. Many times it appears the sound you
hear is coming from overhead when that is not the case.
The sound appears to be omnidirectional. Just as a
subwoofer in a surround sound system cannot be located as to its location. You
can tell where the front right and left speakers are and the
rear right, rear left, and center
channel speakers, but you cannot tell the location of the
subwoofer. Subsonic frequencies are omnidirectional which mean
basically appearing to come from all directions. As opposed to unidirectional
which means
coming from a specific direction that you can tell
the location of by listening.
Essentially sound is vibration that reaches our
eardrums. Underwater this is very muted sounding. Like you are wearing earplugs
which essentially you are. Water ones. Also if you are wearing a hood it further
covers your ears and blocks sounds.
It is possible to hear short words underwater
between divers communicating in close proximity
to each other. I can take my regulator out of my mough and hear myself say short
words. Of course I hear them better than another diver will because I hear the
vibration not
only thru my ears
but thru my jawbones.
For instance you MIGHT be able to understand
someone who takes their regulator out of their mouth and says very
clearly
and pronounciating as sharply and clearly as they
can the word "DANGER" or "HELP" if they clearly SHOUT them. But even these words
are hard to hear via our eardrums and unless you
were right next to the diver and had excellent
hearing you might still not understand exactly what word they said. You heard
them say something but could not understand. Sometimes a diver will yell to
their partner to get their attention if they are right next to each
other. Essentially a shout thru your regulator that
can be heard for a few feet but not forming a word. You can hear a clang or tank
banger underwater
and this is how some divers like myself get our
dive partner's attention. We have an elastic band with a plastic ball around our
tanks and when we want our partner's
attention we pull the ball and let it clang against
our tank so they will look our way. I admit I have no experience as a diver
trying to hear people talking from inside a sub
underwater. But my best guess is MAYBE if you had
your ear right up against the hull you might hear something but whether it would
be understandable or not I do not know.
As you got farther away from the sub I doubt
if you could understand much from even a few feet away although you might hear
sound you might not be able to understand it.
There are underwater loudspeakers I have read
about. But I personally have no experience with them and did not think that was
what you were asking about anyway. I assumed
you meant could you hear and UNDERSTAND without any
special aids or equipment. First the vibration of their speech would have to
reverberate thru the air in the sub and then thru
the hull and then thru the water before it reached
your ears. In my OPINION as a diver, to answer your question directly, if you
were diving right next to the sub's hull and the occupants shouted loudly,
you MIGHT
hear something. Whether or not you could understand
what they said I highly doubt. I'm not an expert on this subject by any means.
Just a diver relating his experiences.
Hope this helped.
Kindest Regards,
Bill Akins.
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