If you were to close your eyes and I moved to a different
spot in the room and made a noise, you would be able to locate my position
without looking. How is that done?
The part of your ear that sticks out from your head (the
Auricle or Pinna) acts as a locater. When a sound is produced the listener
will turn their head until the sound is at its loudest. The loudness is at
its peak when the pinnas are both facing the sound, capturing it and reflecting
it to the small opening into the ear.
Sound travels about 750 miles per hour depending on several
factors. The human brain is fast enough to be able to detect the difference
in arrival times of a sound hitting one ear and then the other. When the
arrival time is the same the observer is facing directly toward or away from
the source of the sound. This is another way a person can tell where sound
is coming from.
When a diver is underwater the pinnas do not function as they do in air.
Since they are almost the same density as the water, and may be covered by
a hood, it's as if they were surgically removed from the head. And, since
the speed of sound in water is about 4 times faster (it is about 3400 miles
per hour) the brain is no longer able to tell the direction of sound underwater.
Sound does travel better underwater. Banging 2 rocks
together can be heard for miles underwater. Contrast that to sound in the
air! So, you will be able to clearly hear your Divemaster banging their tank
to get your attention, but it will not be evident as to where they are