Once again, I am asking questions based on my as of yet defined highly-evolved, human-derived "merfolk". But this time, I'm going towards deeper waters-- let's say about 5000 meters below sea level for now. My "merfolk"'s rough average technological level is roughly analogous to a 1950s-60s Eastern-European/Greek working class towns (I think, it's hard to find a specific equivalent time period for now); with a dash of just enough sci-fi to make it livable enough (think Subnautica). They're so far capable of at least: specially-designed glass and metals to create tools and structures to withstand the pressure, gathering energy from hydrothermal vents and brine pools, and collecting rare ore deposits in the ocean floor. The more advanced places are capable of creating simple submersibles and robotics for specific tasks but these are few and far between, and incredibly costly for an average sea-Joe.

With all that out of the way, I was imagining a way for them to make music and what sort of instruments they could use. They still hold on to traditions from their human ancestors, and so tried to replicate things as much as they could with what they have. Obviously there's a world of difference between sound in the air and in the sea. Vibrations are different, speed is different, distance is different, intensity, scales, etc. Which is why when similar questions are asked, string instruments are usually one of the first to go. Percussion and vocals are typically accepted. But I was wondering, is there a way to engineer a string instrument where it could sound similar in the water as it would on land, or at least be playable? For example, a lyre/harp.

I was actually inspired by the Glass Harp Sponge and wanted the structure to be based on it.

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I considered having metal "strings" made of metals found on deep sea floors that could mimic the look and feel of a traditional harp/lyre (and they'd certainly be better than traditional ones). The bulbs on top could act as resonators of the sound. However, I'm still not sure how the overwhelming pressure of the surrounding water would affect the vibrations/sound. Alternatively, I thought it could be struck like a piano's strings via percussion-- perhaps encased in something to help resonate the vibrations much like the piano's casing.

How can I replicate this "harp" as closely as possible, using my merfolk's current technology?

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    $\begingroup$ Would you be open to a pipe organ that is played like a harp? $\endgroup$ Nov 25, 2023 at 15:47
  • $\begingroup$ @CharlesStaats Well...I originally had this question for instruments in general before settling on strings. Buuuuut, if you have an idea for a deep sea pipe organ I'M ALL EARS. Any excuse to reference POTC Davy Jones is welcomed. $\endgroup$ Nov 25, 2023 at 17:05
  • $\begingroup$ You might be able to adapt an Aeolian harp design to work underwater. Also known as wind harps. en.wikipedia.org/wiki/Aeolian_harp $\endgroup$
    – FlaStorm32
    Nov 26, 2023 at 1:46
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    $\begingroup$ What would be the effect of all this sound on the fish and other creatures? Would whales sing along, or get confused or angry? $\endgroup$
    – FlaStorm32
    Nov 26, 2023 at 1:49
  • $\begingroup$ That's a good question! I was considering that as well. Depending on the instrument and its player it could be pretty disruptive. Or...maybe it could be used to draw them in or locate them. I had the idea of a shepherd for sea mammals, so maybe they can keep track of their herd with the "harp". They can play it and listen for responses. $\endgroup$ Nov 26, 2023 at 2:03

4 Answers 4


Compare this video of "Under the Sea" performed underwater on a piano to a normal piano cover, especially the first 5 seconds of the song. The former version has these completely dead-quiet moments that the latter does not. What is happening is that the vibrating strings in the underwater piano give all their energy into the environment faster than the normal piano, causing them to stop vibrating sooner. This will be true of anything played underwater compared to the air, simply because water is denser than air.

However, can we really say the piano didn't work underwater? Yes, the strings stop vibrating sooner, but they still vibrated and produced sound. It certainly sounds different, but different does not mean bad. Rather than fighting the muting effect of water, why don't you lean into it? Explore what music sounds like when it is physically impossible to hold a note for longer than a fraction of a second. Perhaps merfolk music is extremely fast, with more notes played per second to make up for notes not lasting as long. Perhaps merfolk music-notation reflects the pitch and volume of sounds, rather than pitch and duration. Perhaps music is viewed as an exclusively group activity because individual instruments are unable to consistently fill a soundscape.

Also, a gas-filled cavity is a great way to amplify sound underwater. Many fish make sounds by vibrating muscles or hitting bones connected to the swim bladder (1)(2). Many underwater speakers have air-cavities for similar reasons. A 'harp' based on this would look like a guitar, where the body was sealed and filled with air.

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    $\begingroup$ It could be played like balalaika that already has very short sustain: with rapid plucking or strumming. youtube.com/watch?v=fsfwfW-GOCg $\endgroup$ Nov 24, 2023 at 14:52
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    $\begingroup$ Maybe a piano hammer bouncing back and hitting the string multiple times could produce longer notes. $\endgroup$
    – The_spider
    Nov 24, 2023 at 21:45
  • $\begingroup$ Actually merfolk could just skip instruments that are plucked (guitars) or hammers (keyboard) but use those that are constantly provided with energy, such as with bows (violins), wheels (hurdy-gurdy), or matter streams (pipes, trombones, etc.) $\endgroup$
    – toolforger
    Nov 25, 2023 at 21:58

String instruments would work fine, albeit with a more muted sound, as would many percussion instruments.

You might have seen the Danish orchestra who started doing underwater performances, if not, check out their videos, e.g. this one

As L. Dutch says, the high density of water will means damping will be higher, so you probably want thicker and heavier strings than a typical "air harp" to get any sustain whatsoever. The sound of plucked guitar strings under water is similar to that produced when a guitarist mutes the strings with the back of the palm of their plucking hand. In the video I linked they demonstrate a violin, which is a good example that bowed string instruments are fine. Like Vesper sais: the bow constantly adds energy to the string instead of just adding it momentarily as when the string is pluck.

I would refer to the instrument you describe at the end as a lamellophone(see wikipedia article) rather than a string instrument. (Some people might argue it's an idiophone, but I'd argue they are probably wrong, depending on how the sound would be transfered to the surrounding water.) They work fine under water as well (see video) but have similar issues with shortened sustain. Your rods seem rather long and heavy, so they should be fine. They might need to be mounted on some structure with a larger surface to better transfer the vibrations to the water, but that depends on their precise construction.

If you would combine these ideas, you could possibly end upp with an under-water version of a nail violin, a bowed instrument which was the first thing I thought of when I saw your sponge thing. If you would curve the arms around, so all of them point to the left or to the right, you could use a bow to stroke them induvidually.

  • $\begingroup$ Bowed instruments are fine because the bow causes energy transfer thus the sound of vibrating string does not cease. Plucking a string under water would cause it to nearly instantaneously stop, resulting in a very short sound, I estimate hundredths of a second long. $\endgroup$
    – Vesper
    Nov 23, 2023 at 19:40
  • $\begingroup$ See, I looked up the effects the additional pressure of the DEEP sea would have on sound, and came to conclusion it would be louder. Somehow. Sound travels further in water, and I somehow thought the compression would amplify it's loudness. Maybe I was mistaken? $\endgroup$ Nov 24, 2023 at 16:51
  • $\begingroup$ Sound is a bit different down there, correct. The speed of sound normally decreases when you go deeper, but when you go VERY deep it starts to increase again due to pressure. I'll see if I can expand my answer. $\endgroup$
    – EdvinW
    Nov 24, 2023 at 16:59

Your problem is not the pressure, but the density.

As a 0th order approximation, considering that water is 1000 times denser than air (and water pressure doesn't affect water density appreciably), it will damp vibrations 1000 times more effectively, meaning that obtaining any sound longer than a TAK will become difficult if not impossible.

What can be tried is to let the thing vibrating, and thus producing the sound, in a chamber filled with air, and then have that chamber acoustically coupled with the surrounding water via some mean of impedance matching, which incidentally is how water mammals manage to produce sounds underwater.

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    $\begingroup$ Viscosity rather than density, as it's viscosity that slows down vibrations. Imagine playing a harp in He-II which is superflowing (displays zero viscosity in some experiments, however this might not apply as revolving disks did allow experimenters to get nonzero viscosity for He-II). Not sure however if such a superfluid would cause sound waves from that harp's strings if effective viscosity would be zero, hmm. $\endgroup$
    – Vesper
    Nov 23, 2023 at 19:37

If you want to have something that is played similarly to the harp, I suggest an underwater variation of a hydraulophone — basically a pipe organ that uses water rather than air. Here's what I have in mind:

  • There's some kind of pump that maintains a pressure differential between the inside of the pipes and the outside. Since it is the differential rather than the absolute pressure that matters, this ought to work even if you are very deep underwater (depending on how you drive the pump, of course).
  • Each pipe corresponds to one note. You play the note by touching a key on the pipe that alters the flow of water through the pipe.
  • The key mechanism should be spring-loaded and keep the sound flowing for a period of time before cutting it off (much as some doors close slowly at a constant rate after being opened). Potential variations:
    • Perhaps there is also a percussive element that strikes the pipe, causing it to vibrate more loudly (like a bell) for an instant when you activate the pipe. This extra volume will very quickly be damped down by the water, so you need the water flowing through the pipe for the (softer) sustained sound. [CAVEAT: I don't know how feasible it would be to make the percussive sound both nice and the same pitch as the water-driven sound.]
    • Perhaps you can make the sustained note last for a shorter or longer period of time depending on how far you move the key. One skill of an advanced musician is being able to play an arpeggio and have all the notes of the cord end at the same instant.
    • Perhaps there is a separate key on a pipe you can press to stop the sound. Or even a key that stops the sound in all the pipes at once.

I imagine the result would look something like your Glass Harp Sponge but with something like a clarinet key attached to each pipe. Larger, less-transportable versions would include more pipes, larger pipes for lower pitches, and probably an organ console (or else require multiple players, like a handbell choir).

The point of this whole setup is that the flowing water allows for sustained sound, which is infeasible underwater unless you have some continued source of energy (such as a continuous flow of water or air, or for stringed instruments a bow).

Note that the control mechanisms described here would probably only arise if someone were deliberately trying to reproduce the experience of playing a harp. If the instrument evolved naturally in a sea-dwelling species, you'd probably get something more like an organ console (with perhaps an exotic keyboard) in which a note was sustained only as long as it was held down. Organ stops would allow you to add the bell or chime sounds to make it easier to identify the beginning of a note. I'm basing this on the assumption that real-world pipe organ control mechanisms are probably the most practical way to control instruments like this.


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