Normally, if you hear a sound, you have some idea of where the sound came from. But when a scuba diver hears a sound underwater, it is virtually impossible to tell where it came from.

1. Why?

2. Can you suggest some form of underwater hearing aid type device that would allow more accurate underwater sound localization?

We localize left/right sounds in two ways:

1. The difference in volume between our left and right ears
2. The difference in time between the sound hitting our left and right ears

We also compensate for the fact that lower-frequency sounds are less affected by the difference in distance, but I don't think that's relevent.

As far as I remember, sound travels faster underwater. I assume that this also means that there is a smaller drop in amplitude per unit distance when underwater.

This means that both the difference in time and the difference in volume between our left and right ears is noticably reduced. As our brain is wired for recognizing sound differences that occur in air, we can't correctly compensate for this change. Therefore, we can't localize sound underwater.

This could easily be rectified, however: Take a pair of headphones and attach a mike to each ear. Feed the sound that enters the mikes into a machine that 1) delays the second sound by a few ms (or however much), and 2) reduces the volume of the second sound by some amount. If the device is correctly calibrated, it should make sound localization possible again.

Up/down localizations, performed by the outer structure of our ears (as are, I think, front/back localization) are a different kettle of fish entirely.

Edit: apparently the speed of sound in water is five times faster than that of sound in air. So the machine should delay the second sound by 5x the original amount (adjusted for the tempurature of the water, if possible). Probably something along those lines for the change in volume, but I don't feel like calculating it.

Edited on April 14, 2005, 10:27 am

Posted by Sam on 2005-04-14 10:15:40