Human ears are mostly useless regarding underwater listening. It’s comparable to the regular microphone that doesn’t function well underwater, the reason is a poor impedance match between the construction materials of the auditory device and the propagation medium.
“In the water, the audience picks up the sound only by the effect of bone conduction. Basic principles: In immersion, the ear drum (tympani) is too close to the density of the water to stop any sound wave (the ear drum is made of 90% water). Only the bones are hard enough to stop the fast sound waves (1450 m/s, four times the speed of sound in the air). So, the bones from the neck and skull resonate and carry the vibrations simultaneously to both of the inner ears, the nerves’ endings located in the skull”
[Michel Redolfi, an interview after a Festival “ARS ELECTRONICA”].
Instead of two medias (human ears), there is only one medium underwater which is skull.
“A listener in the water doesn’t hear in stereo so he loses his sense of direction, [and] Cartesian space (Left-Right/Up-Down) dissolves. Space is not ‘mono,’ but omniphonic (sounds seem to be coming from all around). Psycho-acoustically, this loss of Cartesian space translates in one’s mind as an inner vibration that would come from inside the body… Interpretation of this feeling varies depending on people’s beliefs, fantasies, and poetic feelings…” [Redolfi].
“[Sound underwater] doesn’t really travel through your eardrums. It automatically vibrates the skull, and from that, your ears.”
[Joel Cahen, the UK-based sound and visual designer who founded the traveling “deep listening” event Wet Sounds. ]
And since underwater sound is picked up by direct vibrations of inner ear nerves, it inevitably sounds – and feels – more immediate.
Thus, stereo perception is not possible and sounds will lack direction cues. Since the human observer is the vibrating apparatus, however, the reception is not that of a mono signal but of a signal coming from all directions at once:
“A listener in the water doesn’t hear in stereo so he loses his sense of direction, [and] Cartesian space (Left-Right/Up-Down) dissolves. Space is not ‘mono,’ but omniphonic (sounds seem to be coming from all around). Psycho-acoustically, this loss of Cartesian space translates in one’s mind as an inner vibration that would come from inside the body… Interpretation of this feeling varies depending on people’s beliefs, fantasies, and poetic feelings…” [Redolfi].
In addition, a bone conduction occurs to behave like a low – end filtering of the underwater sound spectrum:
“Thanks to bone conduction, a radical filtering operates on the sounds that we listen to in the water. The bone equalization brings an emphasis on medium to high frequencies, while basses are completely ignored. The underwater sound world appears very crisp, crystal-like” [Redolfi].
“For some reason, I thought that sound underwater would be like in the movies… kind of muffled,” he says. “But actually it’s super sharp and really clear – really, really, super clear.” – Joel Cahen
This leads to another point – underwater we are not in touch with noises from the air and since underwater noises are not strong enough to generate the skull, what we hear is very pure.
“While we have our head in contact with sonic waters, our bone conduction apparatus doesn’t pick up air noises, nor water background noises as they are not strong enough to resonate in the body. In a pool those unheard noises are actually generated by pumps; at sea by boat propellers, wave foam, etc… The only thing you hear in the water is a pure signal as if you were listening with headphones. This very close encounter with the soundscape was called ‘HI-FI’ by Murray Shafer, the Canadian musicologist and composer who conceived the theory of Soundscapes back in the seventies. He was referring to Hi-Fi natural soundscapes such as the ones of remote mountains or deserts. Lo-Fi in comparison applies to street soundscapes…” [Redolfi]
Summary:
- Underwater sound is picked up by the effect of bone conduction. That means the bones from the neck and skull resonate and carry the vibrations to both on inner ears at this same time.
- Human perceive space underwater “omniphonic” ( sounds are coming from each direction). We can’t talk about “mono” or “stereo” perception.
- The underwater sound appears very crisp. It’s because of low-end filtering characteristics of bone conduction. The bone equalisation brings and emphasis on medium to high frequencies.
- The only thing you hear in the water is a pure signal as if you were listening with headphones.
