Hello guys . This is my first post on this forum 
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I am looking for the easiest way to generate acoustic waves underwater for an experiment , between 200Hz and 20000Hz ( the audible range ) .
Is there a way to use a normal speaker and to waterproof it , as in put it in an enclosure and use a waterproof membrane ?
.I am looking for the easiest way to generate acoustic waves underwater for an experiment , between 200Hz and 20000Hz ( the audible range ) .
Is there a way to use a normal speaker and to waterproof it , as in put it in an enclosure and use a waterproof membrane ?
Way back during some of my early student days, I used something called a "sonicator" to dissolve clays in water. It was basically a steel rod that could be excited at manually adjustable frequencies.
I've also seen some cool hand's on museum/discovery center exhibits that simply elevate bowls of water over big woofers to illustrate eigenmodes, etc. I've thought about doing this at home as a party trick.
I've also seen some cool hand's on museum/discovery center exhibits that simply elevate bowls of water over big woofers to illustrate eigenmodes, etc. I've thought about doing this at home as a party trick.
I have been to a hotel where there are speakers mounted in the swimming pool under water. They were quite large, maybe 10 or 12 inches. The bass could be felt when swimming near one, and the music was audible through the entire pool. No idea where they came from.
Back in the early 70's I took a pair of Poly planar speakers, mounted them to a piece of plywood and added some Styrofoam for flotation. The entire thing was tossed into the Atlantic Ocean off the back of a 34 foot sailboat and connected by about 25 feet of speaker wire to the 8 track player in the boat. The music was reasonably loud and could be heard to a depth of 15 to 20 feet.
Poly Planar speakers are still being made, but I have no idea if it is the same company, but the concept looks similar. These are very expensive, the stuff I used in the 70's was like $20 each at Olson's Electronics (like Radio Shack) flat panel speakers with Styrofoam cones and plastic frames.
Polyplanar LLC. – Waterproof Marine Audio Systems
Back in the early 70's I took a pair of Poly planar speakers, mounted them to a piece of plywood and added some Styrofoam for flotation. The entire thing was tossed into the Atlantic Ocean off the back of a 34 foot sailboat and connected by about 25 feet of speaker wire to the 8 track player in the boat. The music was reasonably loud and could be heard to a depth of 15 to 20 feet.
Poly Planar speakers are still being made, but I have no idea if it is the same company, but the concept looks similar. These are very expensive, the stuff I used in the 70's was like $20 each at Olson's Electronics (like Radio Shack) flat panel speakers with Styrofoam cones and plastic frames.
Polyplanar LLC. – Waterproof Marine Audio Systems
The speed of sound in water is about 1500m/s or a little under 5 times in air. So the wavelengths are huge at 200Hz. Military sonars can be huge arrays covering almost the length of the ship. The longer wavelengths traver further but have poorer resolution.
But sound travels easy under water so u prbably will get sound at 200Hz without having a 2m diameter speaker.
I would try bolting a 12" or so to a larger surface. Have that surface into the water. Of course making it like a box so water stays out. Or maybe an empty oil drum. Use the bottom surface down in water. Just anything that can vibrate but keeps water out.
But sound travels easy under water so u prbably will get sound at 200Hz without having a 2m diameter speaker.
I would try bolting a 12" or so to a larger surface. Have that surface into the water. Of course making it like a box so water stays out. Or maybe an empty oil drum. Use the bottom surface down in water. Just anything that can vibrate but keeps water out.
" Just anything that can vibrate but keeps water out.". I ve been told that I will need insane amounts of power since water density is huge compared to air density, and the speaker will be used to vibrate air that will then vibrate a membrane or something. Will that actually pose a big problem?
Maybe something like this Dayton Audio HDN-8 Weatherproof Sound Exciter Transducer ? and attach it to the inside of a suitable enclosure
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The speakers we used in the 70's were fed from a car 8 track player, maybe 8 watts on a good day. The speakers we used, however had their Styrofoam cones in direct contact with the water. Anything with air between the cone and the water will be very lossy and have frequency response issues since the air is a compressible medium.
They were used for over a year before they fell apart. Their demise seemed to be more from sun damage than the water. We tried not to get the back side where the magnet was wet, but it did get constantly baked by the sun and the plastic frames got brittle.
A quick Google search for underwater speakers for pools returns several hits, but all are expensive. Oddly one of the cheaper ones comes from a well known speaker company, Electro Voice.....still over $300
Electro-Voice UW30 30-Watt Underwater Flush Mount Speaker (8 Ohms/Pool Blue) - Newegg.com
Clark Synthesis AQ339 Diluvio Underwater Speaker
They were used for over a year before they fell apart. Their demise seemed to be more from sun damage than the water. We tried not to get the back side where the magnet was wet, but it did get constantly baked by the sun and the plastic frames got brittle.
A quick Google search for underwater speakers for pools returns several hits, but all are expensive. Oddly one of the cheaper ones comes from a well known speaker company, Electro Voice.....still over $300
Electro-Voice UW30 30-Watt Underwater Flush Mount Speaker (8 Ohms/Pool Blue) - Newegg.com
Clark Synthesis AQ339 Diluvio Underwater Speaker
I dont mean have the speaker inside playing and the sound thru the air then should couple into the surface of your box to make it vibrate.
I mean mechanically couple the speaker to the bottom of your whatever, so the speaker just becomes one with it and makes the box/oil drum vibrate that way.
The mass of water will rip apart a speaker made water proof with a condom wrapping or what ever.
You need to secure the speaker frame to the sides/back, the membrane or coil the somehow mechanically fastened to the bottom (the surface which you want to make sound), to make the bottom play along. A large mass fastened (glued?) to the magnet/back of speaker helps getting the energy into the bottom (so the speaker frame/magnet moves less)
I dont know, but it's just one suggestion of transferring sound from a normal speaker driver to something that doesnt get ruined by water.
You mentioned underwater, but you didn't say much about the premises.
It would help to know if it's in the middle of the ocean, a swimming pool of size with cement walls, a small aquarium with glass or plexiglass walls, etc...
If it's like an aquarium, you could just attach exciters to the outside of the wall, the whole wall acting as the speaker.
If it's more like a big cement swimming pool, or the middle of the ocean, make a small sealed plywood or clear plexiglass box, attach an exciter on one of the inside wall, add weights and dump it in the water. For the amp, use Bluetooth for sending the signal and put the amp and battery to power it inside the box, or run a cable to outside and power from a dry location.
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