[music-dsp] underwater sound

[Bram de Jong]

On Mon, 14 Jun 2004, Nicklas Marelius wrote:

> Just curious as to what your thoughts are on audio playing underwater.

Aah you'er lucky as I did some info-gathering on the subject:

* most important fact is that your ears are useless underwater: the 
impedance of the membrane in your ear matches the impedance for air, but 
not for water. Under water you hear with your BONES!
You can test this in a swiming pool: take something metal with you nd ask 
a kried to bang it against the pool walls. You can close your ears with 
your fingers, but it won't make any difference.

* a result from the above is that you can't hear any low tones under 
water. Think of it like a high-pass filter on anything. This also results 
in loss of dynamics.

* the high tones -not being obstructed by anything- will sound VERY clear 
and almost perfect -so I've read-

* audio is mono only under water: sound travels a lot faster under water, 
and as your ears rely on phase differences -which are a lot smaller under 
water due to the speed-

* swiming poolar are VERY bad audio environments: hard walls, VERY 
rectangular... It's a big reverberation tank. However sound travels 
faster, so you have to scale dimentions.

* The only way to play audio under water is by using specialised speakers, 
with impedance matched to the impedance of water! (called hydrophones)

* sound reflecting on the surface of water seems to have little effect on 
sound, except if we're talking ocean-size waves. As far as I've read they 
introduce a sort of fm-modulated effect.

* As a result of the impedance of water - I think - it's hard to make 
sound under water without the right equipment, but this has an advantage: 
if you DO have the right equipment all OTHER sound is completely drowned 
-pun intended- by the audio from the speakers: you have creastal-clear 
audio, so no anoying truck-passing-by sounds like you would have in 
your home ;-)


Summary: sticking your head in a bucket ain't gonna work ;-) It would be 
funny though, so please do so, and send us some pictures.

Ah, and, could you add all of this to the musicdsp.org Wiki ;-)
(after others have corrected / added)


 - bram