View Full Version : Swimming pool physics #1

2005-Jan-10, 11:06 AM
Yesterday I went to a newly reopened indoor pool (http://www.vierordtbad.info/0start.htm) just down the street where I live. Very convenient. It's one of the oldes indoor baths here, but completely renovated in the last two years.
Due to extensive exposure to BABB, I didn't simply relax there (note: make entry into YKYAABABBAW-thread), but made some observations I'd thought I can post here.
Here's the first one (the second one is here (http://www.badastronomy.com/phpBB/viewtopic.php?t=18850)):
They installed some underwater loudspeakers, so while diving you can listen to some nice music. I recognized the music was in my head, I couldn't make out where the speakers were, no direction detectable.
I concluded, that due to the high velocity of sound in water (some 1450m/s, 4.5 times faster than in air), the temporal difference between soundwaves in the left and right ear may be too small to help with getting a direction.
Can this be the point? Or is it normally possible to locate a sound source under water?


2005-Jan-10, 11:24 AM
The ears determine the location of a sound by the timing difference between the two ears. In water the speed of sound is too high to make this work (too little difference in timing). It is a well known effect to scuba divers, you can attract the attention of another diver by banging something but he can't locate you by the sound alone.

2005-Jan-10, 11:25 AM
If there were more than one speaker underwater it may be that it's not possible to distinguish the different directions. I don't see why steroscopic sound shouldn't work underwater, IIRC it's not phase difference that gives the direction but volume level. It's also an unfamilliar enviornment. It's difficult to scream for help while your drowning and subjectively listen to music as well :lol:

Edit: Just read Zebo's reply and I drown corrected 8)

2005-Jan-10, 11:26 AM
There are likely to be multiple speakers in the pool, plus, the sound would reflect off of the walls of the pool around you, which would mean it would be more difficult to locate sound sources. Same as it is in a room with 4.1 or better surround sound.

Sound is directional under water, though. Be under water when someone does a cannonball at the other end of the pool. You'll hear it.

Kaptain K
2005-Jan-10, 04:29 PM
IIRC it's not phase difference that gives the direction but volume level.
Actually, it's both (or either - the brain has a remarkable ability to make do with whatever data is available).

2005-Jan-10, 04:38 PM
This reminds me of trying to explain stereoscopic vision to Humphrey the other day, for depth perception. It's a combination of your two eyes looking at an object and just from remember how large an object is and then seeing it far away. - Colt