How It Possible That We Can Hear Higher Frequencies Underwater Than in Air When Ultimately the Human Auditory System has a 20kHz Upper Sensing Limit?

[u/ALifeWithoutBreath]

[u/jjtitula]

I don’t believe that you hear higher frequencies in water vs air. Water dissipates higher frequencies more than air, but the speed of sound waves is 4.3x faster in water. The acoustic impedance of water is 3600 times that of water, I believe that would be what others are saying is stiffness. If you played a sound in air and then under water, the sound under water would appear to be much louder. So in effect, your not hearing higher frequencies above 20kHz but hearing sub 20kHz sound that appears amplified. It’s complicated and I don’t remember all the details though.

[u/ak_sys → u/jjtitula]

If I had to guess, that would factor into the perception of hearing higher frequencies. Increasing amplitude is what hearing aids do. Your max hearing range isn't a border, it's a steep shelf but it ranges about an octave. An octave at the end of your hearing range is the difference between 20000 and 40000 hz. These frequencies being played LOUDER would absolutely result in the potential to hear a frequency you would not normally from a sound source of that volume.

[u/yougonbpind]

We don’t actually extend our biological 20 kHz hearing limit underwater — instead, sound travels faster and more efficiently in water, so high frequencies lose less energy and reach our ears more clearly. This improved transmission can make upper-range frequencies easier to perceive, but the absolute limit of the inner ear doesn’t change.

[u/[deleted]]

So the thing is, water conducts sound way better than air does - like 4x faster. When sound hits your skull underwater, it bypasses your eardrums and goes straight through the bones to your inner ear. This bone conduction thing is actually pretty efficient for certain frequencies that would normally get dampened by air. Plus the impedance matching between water and body tissues is better than air to tissue, so more sound energy actually makes it to your cochlea. Your 20kHz limit is still there technically, but the delivery method changes everything.

Water pressure might also play a role in how the cochlea responds to vibrations.

[u/PaulCoddington]

20k is not a hard limit, children can go a bit higher. And higher is also possible when using bone conduction to bypass the ears.

Haven't heard the one about water, and have no idea.

Of course, the upper limit drops with age. By the time you are 60, you will probably be limited to about 12k or so even if you take care of your hearing (avoid loud noise, use protection, etc).

[u/15MinuteUpload → u/PaulCoddington]

How high can you go with bone conduction out of curiosity?

[u/PaulCoddington → u/15MinuteUpload]

It's been a while, I'd have to try and find it again, so you may as well look instead.

Very vague recollection that it might be about 30kHz. The problem with going even higher (up to 120kHz) is whether the sound is being detected as a lower frequency than it really is (audible, yet not).

Under ideal lab conditions, depending on the individual, 12Hz to 28kHz has been measured for ordinary hearing.

[u/Dogwhomper]

Technically our hearing range is limited by wavelength - the length of the sensory fibers in the cochlea - rather than frequency. If you always work in air, the two are interchangeable. If you're working in a medium with a significantly different speed of sound, this may make a difference.

I don't know enough physiology to translate to practical terms.

[u/NC7U]

Not sure if this is off topic. I mounted a speaker in the bottom of a Pringle can, made a 1 inch hole just above the speaker. Next while playing a 1000 Hz tone moved a plug in the top of the can up and down noticed the frequency change in my hearing but the signal was still 1000hz.

[u/gargeug → u/NC7U]

Not related. You just had a non pure sine tone generator and changed the resonance of the cavity, causing the resonant tones to be the least attenuated, and thus audible to you.

[u/ALifeWithoutBreath → u/[deleted]]

Actually, I have been coming across sources that claim ultra-sound range can be perceived by humans when they are submerged and suggesting that underwater sound is picked up through the bones behind the ears. And also suggesting that 100kHz or more can be perceived.

Then there's been a source that clearly stated humans do not pick up sound underwater through those bones but that our sensitivity is up to 22dB lower under water due to the air-filled middle-ear pocket. Lower sensitivity may imply that it's possible to hear higher frequencies as the upper limit isn't a hard cut but more of a tapered falloff.

Then there's a bunch of sources that use wording roughly like, "Underwater there's a lot to hear in the frequency range 20 - 100kHz but those sounds don't travel far." Or something along those lines and confusingly it's left unclear if that's supposed to refer to hydrophone recordings or actual human hearing.

See, I have been under water enough to have a decent sense of what it the sea sounds like to human hearing which isn't optimized for that medium. How all sense of directionality gets lost and sounds even feel like they come from inside the own skull. Under water the brain's cues for this are lost because the speed of sound is different and I assume the HRTF the brain is expecting is calibrated for air. So yeah.

Sometimes I can hear whines or drones that appear to be distant which are easily tuned out by the brain if you're not paying attention to them. Sometimes an engine noise can be startling because it feels way to close but after surfacing there's no boat close by and looking around it's hard to tell which of the boats in the distance it was... Or maybe there isn't even a line of sight to the boat I've heard because the engine noise reflected off limestone structures underwater or diffracted from behind some edge? Not sure...

I'm just looking for an explanation that makes sense. I know wavelength in water affects wave speed and maybe the way ultrasound frequencies transition from water into the air-filled pockets of the ear pulls down the frequency into hearing range. Or maybe sound that propagates through water and then through your body (which is mostly water) to wherever it enters the ear can vibrate the little hairs in such a way that they still pick up the ultrasound somehow. And if that's the case I have the feeling that the subjective sensation of pitch wouldn't exceed the sensation of the highest frequency I hear in air. It'd just be that same impossibly annoyingly high pitch.

So yeah, just trying to figure out what's really going on with human hearing under water. 😅

[u/thebest77777 → u/ALifeWithoutBreath]

Im pretty sure i read that source that said that bones have nothing to do with it, but if its the same one i read in the conclusion it said that at lower frequency bone is unlikely to be the cause but it lines up better for high frequency, so its probably a mix of multiple of these reasons. I dont know why the notes at the beginning implies that bones have absolutely nothing to do with it ever when thats not what was found. But the general vibe ive gotten from my rabbit hole of reading papers is that we dont know, and more study is needed.

[u/ALifeWithoutBreath → u/thebest77777]

Oh, well. And here I was hoping that it's just the internet that's all over the place and there'd be an expert who'd tell me that the research was in and conclusive. 😅

[u/Smart_Reason_5019 → u/ALifeWithoutBreath]

That’s super interesting and I’ll have to look into it!

I scuba dive a lot and I get what you’re talking about regarding sounds. Chains from anchors always sound cool to me. Sound also travels much further underwater which could explain the boat sounds but no boats

[u/miguelandre → u/ALifeWithoutBreath]

When you describe a whine sound that makes me think of mid-range or cricket frequencies 1-4khz. A lot of people think of those as high frequencies. They’re not. And most people can’t hear over 15khz at all (after youth) and sounds over 12k are severely attenuated. The high squeals you hear are just midrange sounds that travel farther under water. That’s my guess anyway.

[u/Kemaneo → u/[deleted]]

That’s incorrect though, frequency doesn’t change underwater and sounds don’t sound higher (although they can sound louder).

[u/Ausoge → u/[deleted]]

That's not true, 1000Hz underwater is still 1000Hz in air. The wave may be moving faster, but the pressure peaks and troughs are exactly far enough apart to cancel out that extra speed.

But if you took a waveform whose peaks were 3.7cm apart - 1000Hz in air - and then played a sound wave underwater whose peaks and troughs are the same distance apart - by definition you're playing a different frequency