Now You Can Record Mermaids Singing

Buy stock in hot glue, this project corners the market on the stuff. [Leafcutter John] uses the hot goop as his water-proofer of choice when building an underwater microphone (also known as a hydrophone). By installing a couple of piezo elements on one lid of a tin can he is able to record some amazingly clear audio. This is aided by a pre-amp inside the metal enclosure. By cleaning off the clear coating from the inside of these steel can parts, he was able to solder the seams to keep the water out.  In the end, coins are added for ballast and any remaining space is completely filled with hot glue.

He’s got a handful of example recordings on his project page. Here’s an what a running faucet sounds like from under water:

34 thoughts on “Now You Can Record Mermaids Singing

  1. What might also be good for filler instead of hot glue is the material used to make water in model train sets. You can buy it at hobby stores in big bags, it melts at a low temperature and has a slightly harder consistency when cooled. I suspect it would be cheaper by volume than hot glue, so might be more suited to be used as filler.

  2. I better filler might be canning wax. You can buy a brick of it for about $3 or so. You could drill a hole in the side, melt a brick of wax in a small saucepan, and pour in through a funnel.

    Stick of glue are expensive unless you sell them wholesale (like my company).

    Interesting project, though.

  3. Hot glue FTW!
    I consider the stuff right up there with duct tape in terms of potential uses. Have a burst blister, paper cut, or (even worse) a cardboard cut… cover with glue from a low temp glue gun and you’re as good as new. I’ve never found anything else that works as well.

  4. @ SSquire ADC? Wasn’t that a preamp in the eclosure?
    pretty much needed,if a cord of any length is needed. Also my guess is that the can side is anessential part of thr microphone.

    i think it would be far out to suspend this from buoy, and use a walkie talkie to send the audio to shore, where a good audio filter computer app could be use to filter. A nice find

    Mike, a great post for hackaday

  5. From the initial HAD description I thought the preamp was going to be completely covered in hot glue too.

    From what I’ve seen some people think using hot glue isn’t a viable tool, like it’s not good enough or something, but if you’ve opened electronic things to repair etc. you’ll have seen just how much hot glue is used in everyday electronics.

    Like shown in the hack, it’s especially good for securing cables so they don’t get ripped out of your project.

    It’s a great substance, if you want to do small spots where your glue gun can only do large globules, cut off a piece of the stick, place the piece where you want to hold something down (usually thin wire for me) then point a hot air soldering iron at it :)

  6. The acoustic coupling will be best if the material is as incompressible as possible. Hot glue and other viscoelastic polyolefins are both soft and dissipate sound readily. Using acrylic casting resin might be the best acoustic impedance-matching material that is readily available.

    Has he thought of using these as speakers? In-tub stereo for that (wait for it)… immersive sound?

  7. Another trick for underwater electronics is to fill the enclosure with mineral oil. Fairly cheap, and if you close the project box when submerged in oil, you can avoid almost any air being trapped inside. Not much good if you want to solder your container closed, but great if you have a project box with a gasket, and want to bring it down below a couple of metres. A light coating of epoxy/hot glue/polyeurathane/etc over internal electronics is still recommended in case you submerge it too far and a little water leaks in, but you don’t need to encase it in a block of the stuff.

  8. @SSquire.
    If you call ADC to the pre-amp, this will be on the wet side because the cable add more noise and low the gain (you don’t want to amplify the noise, no?)

    The other option is use this contact microphone attached to a pice of aluminium and made a housing using acrylic (you can use acetone to glue the acrylic) and a rubber joint to insolete the acrylic and aluminium plate to the water

  9. Just to clarify, the preamp does end up totally covered in hot glue once it’s sealed ballast is added to make it sink.

    The preamp is definitely needed. It matches the high impedance of the Piezo element which gives a better sound (more bass). Preamp is in the enclosure to keep the piezo wires as short as possible which reduces noise. The cable coming out of the tin can then be as long as needed (see what i did there)

    As for hot glue, i think it works well for this purpose, and it wont burn you unless you get a sizable blob on you, then it f*&%^n hurts as macegr will attest. I agree with Scott that a harder material may be better for the sound.

    The water sample does sound tinny, I actually stuck my head in the sink and listened to that sound. Guess what, it sounded really tinny. The Rubber duck sample on my page sounds much better to my ears.

  10. I know this guy that did some sound recording for Pirates of the Caribbean. What he did is got a portable sound recorder, put it in a condom, then tied up the end, then walked out into the sea and recorded about half an hour of sounds. He got payed about $10,000 to do it.

  11. 3M Scotchcast 2130 or 2135 works better than hot glue and can withstand pressure up to 3000m salt water easily. For the best sound quality however the actual ceramic mic should be in castor oil enclosed in a piece of fuel rated clear vinyl tubing at a pressure of 3-5 psi over atm. God Tier – leave the castor oil under pressure (1.46 psi per m of expected depth.) for 24 hour to purge dissolved gases. This will help keep the water pressure from crushing the tube.

  12. @D- & @Peleca, sorry I said ADC out of habit as they’re usually built into the ADC boards. Of course, I see “more bass” in another comment and quickly understand we’re listening for very different things. ;-)

  13. @macegr

    No I wasn’t joking actually. Based on your pic, you had a large amount of glue touch you at the same time… that’s a lot of heat! You can handle something very hot as long as it is in small amounts. Splashes of boiling water sting for a second (or not at all on hands) because they cool so fast. I probably should have added that to my first post… disclaimer: Don’t try to speed up the “healing” process by dunking the entire area into hot glue in a single step. lol!

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