Hydrophone and Underwater Voice Communications
Step by Step Instructions for Building a Deep Diving Hydrophone and 2 Way Voice Communication System for Under $50
Use it in a submarine to keep in touch with your surface support vessel or listen for boats before you surface. Use it on an ROV and record underwater sounds, and even play sounds back to attract and study how animals react.
David Bartsch spend eight years in the Navy and made thirteen deterrent patrols aboard the ballistic missile submarine U.S.S. Kamehameha (SSBN642B) as a sonar technician. Now he is making DIY Sonar for the rest of us.
David will be glad to answer any questions you have, and
he'll even build the unit for you. The voice communications consoles
go for $245.00
and the collision avoidance sonars are $160.00 plus shipping.
You can reach David at
In WWII German submarines sank thousands of ships transporting troops and equipment across the North Atlantic to England. The answer for the Allies, came in part from "SONAR", short for Sound Navigation And Ranging.
There are two distinct forms of sonar: active and passive.
Active sonar transmits a "ping" into the water and then listens for the sound waves to return after they bounce off objects like submarines. Onboard electronics than measure the time from when the "ping" was sent out to when the echoed sound is received. Sound travels around 343 meters per second through water, so if the sound returns in 2 seconds, the the submarine is 343 meters away. One second for the sound to reach the target, and one second for it to return. A simple fish finder or fathometer is an example of an active sonar system, but during WWII this was cutting edge technology.
Passive sonar does not transmit sound into the water but relies on the sound already in the water. Every ship makes sounds with its propellers, onboard equipment and movement through the waves. And no two ship sound exactly alike. All the noises produced by a ship are called it's "signature." The Navy's expensive passive sonars keep recordings of ship signatures, and tell the sonar operator the type of ship and possibly the actual name of the ship it has detected. You may a have seen this in Hollywood movies. Sometimes its not all science fiction!
The hydrophone is a microphone made for use underwater. The heart of any sonar is its hydrophone because the sonar can only be as good as it's ability to pick up sound in the water. The main part of a hydrophone is it's transducer. The transducer converts sound waves or the mechanical sound energy into minute electrical energy that can then be amplified. In the early development sonars used naturally formed crystals that when excited produced small (AC) electrical current. Today, piezo technology has replaced crystals in hydrophone transducers.
Piezo elements are man made crystals, easily produced in a controlled environment and cheap. We got a pack of 10, quarter sized piezo disc off eBay for $5.
The piezo elements can both transmit and receive, and they are
used that way in fish finders, but for a hydrophone, we only need to
listen so we only use the piezo to convert sound into electric
current that is then sent to an amplifier and then a speaker.
A Hydrophone for Collision Avoidance
One of the greatest dangers in a mini sub is getting hit by a speed boat as you approach the surface. A boat will easily shatter acrylic view ports causing the sub to flood and likely killing the crew. The hydrophone amplifies the sounds of boat props while the sub is still at a safe depth so the crew know when the surface is clear to surface.
If you scuba dive then you know how easy it is to hear a boats props but that sound does not transfer well through a submarines hull and on to the crew inside a submarine. You also know that it is very difficult to determine the direction of the sound. The hydrophone lets the crew easily hear boats, but it is also somewhat directional so it also helps the crew determine the direction of the sound.
Hearing the boat is critical and the way sound travels underwater can be deceptive. When a layer of warm water forms at the surface it has less density that the colder water below. The change in density causes sound to bend or refract just as light does in water. This traps sound is what is called the "surface duct". Imagine that you in a mini sub having just explored a reef down to the cold waters at 230 feet. Now read to end your dive you stop all motors and listen for surface traffic but cannot detect any. You begin going shallow and start picking up speed as your ballast tanks are blown dry at 80 feet. All of a sudden as you pass 40 feet a loud surface contact is detected that seemed to come from nowhere! How? The noise it was generating was being reflected by the change of temperature back towards the surface and was trapped in a surface duct.
The collision avoidance hydrophone is also the listening half for David's 2-way underwater voice communication system. When the speaker system is added along with a second system on a surface craft then the submarine crew can remain in voice communication with the surface during a dive and down to 500 feet. The hydrophone is quite small but picks up waterborne ambient noises very well.
(1) The hydrophone is placed on top of the sub, preferably on top of the sail, and faced upward at a 25 to 30 degree angle where it can best detect boat traffic. (2) The small control box; black and just to upper left of seat is mounted against the hull using a large magnet. The speaker is just above the air tank. (3) The controls include a power switch, a single gain and volume control knob.
Kyle funded this initial sonar and has successfully tested it. as shown in the video.
When it comes to the amplification there are many options. Here are a few:
Option #1: (3) Electronic Kits, www.electronickits.com has and 18 watt amplifier for $20, and it will not need a preamp unless the cable length is more than 6 feet. The hydrophone connects to the amplifier along with power from the 12 volt battery and the output connects to the speaker. An 8 ohm speakers from a discarded stereo will do nicely.
Option #2: (4) All Electronics,
www.allelectronics.com has a mono (not stereo) pre-amp kit for
$13. The hydrophone is connected to this first along with a
battery for power. The pot on the board in the pre-amp kit adjust
gain. This pot can be replaced with a pot on the control box so gain
can be easily adjusted along with the volume from the amplifier. (5)
The signal from the preamp can then be feed to a 7 watt mono
amplifier kit for $16 and the dives a speaker or the 18 watt amp.
A preamplifier is really used to boost this initial signal so as to avoid loss during transit to the amplifier itself. With this signal left low, cross talk and interference could result especially during long runs like on larger submarines. Preamplifiers are not actually required but do boost the output slightly. Both the preamp and the amp are supplied with the same 12 vdc power and this is controlled by a single power switch.
Option #3: (4) Get the pre-amp kit for $13 from www.allelectronics.com and connect it to a Battery powered portable 5 watt amplifier.
Option #4 (6) Just buy a battery powered guitar amplifier. A Lyon 5W portable amplifier will cost less than $30 (2009) and they work great. The hydrophone is simply an analog microphone that can plug into any off-the-shelf equipment that takes a microphone, such as a PA System, guitar amp, or your PC. The big advantage of a guitar amp, is that they are available as battery powered units, and so easy to take with you. Many, like the Lyon 5W amp even have a jack in the back for your MP3 player and you don't even need the second speaker.
This is also a simple camera and light housing that can survive to 700 feet. It's roomy, so you can put a preamp inside too and have the signal boosted so it can run across a cable longer that 15 feet.
(1) (2) (3) (4) David's HBH-2 hydrophone is uses a PVC coupler with o-rings that seal aluminum back on one end and a 5mm thick piece of acrylic or Plexiglas on the forward end. The piezo is adhered to the acrylic with superglue and bolts pull the two ends tight against the o-rings.
(5) (6) Using a 3 1/4" diameter (83mm) hole saw. Anything smaller will not allow enough room for the mounting bolts to clear the o-ring.
Ti takes time to rattle off one of those 2 mm aluminum disks used as a back wafer to the hydrophone. The guide hole will be drilled larger to accommodate a standard compression fitting and the eight hardware mounting bolt holes will be drilled later.
A hole saw is intended for use on wood, but after having made numerous aluminum disks, it still shows no wear. Harder metal will not have the same results I'm sure.
The acrylic wafers are cut with the same hole saw, but with the center drill bit removed. Use clamps and go slow. The cutting blade will actually melt it's way through the acrylic.
(7) (8) The rough edges of the aluminum and the acrylic can be removed with sanding.
This HBH-2 hydrophone was used as part of the underwater voice communications prototype system so for more detail see the Build Your Own Underwater Voice Communication System - Video Series below.
If you only need to house the piezo for the hydrophone, then another option is to use a single metal or PVC ring to support an single o-ring that is compressed between two wafers. You also don't have to use acrylic, the wafers can be metal too. This a version would be good to thousands of feet.
This very small enclosure was sent into "The tongue of the ocean" near the Bahamas and went all the way down to 1273 feet without flooding! It would have gone much further, but the tester ran out of fishing line. :)
The piezo element is super glued to the inside surface of the Plexiglas and its interface cable is pass thru the aluminum with a standard compression fitting. A generous application of plumbers goop for good measure and your done. You do need a really steady hand to make this one.
Need something quick and extremely simple? You can simply connect the piezo to the wires and the dip it in Plasti-Dip or coat it with a layer of silicon or Goop. It will work almost as well a unit that is inside an air chamber.
When you install the hydrophone on a submarine or ROV you will want to isolate it from the hull with silicone, neoprene or some other flexible material so you don't hear every movement from you or motors. However some sound from the hull is a great way to tell that you are scraping up against something you may not have seen.
Some kind folks a NOAA have published a paper for building a towed hydrophone array. If you want to find and listen in on whales and dolphins, this is a great way to go. Click here to download: A Guide to Constructing Hydrophones and Hydrophone Aarrays for Monitoring Marine Mammal Vocalizations. It's totally DIY, but they have a really nice budget. You can likely reduce the potted volume and save some money on this project.
The underwater voice communication system consist of an underwater speaker or solids transducer wired to an amplifier an then to a microphone. You simply activate and speak into the microphone and your voice is amplified and sent to the transducer and broadcast into the water just like a public address system would use speakers to broadcast you voice into the air.
Divers in the water around you will be able to hear and understand what you said buy your voice can travel hundreds of feet to a boat on the surface. The sound will be very faint when it reaches the boat so at the boat is an underwater microphone or hydrophone. The hydrophone will pick up the faint sound, run it through an amplifier is and the to regular speakers. When we give the boat crew a microphone, amplifier, and solids transducer that the divers or submarine crew a hydrophone, amplifier, and normal speaker or ear bud, then you have a complete two way underwater voice communication system.
We purchase two "Sounds-Star" audio transducers on eBay for under $60 for both. Although commonly classed with speakers is not a speaker. It is a sound transducer for solids, a means of causing structural solids to reproduce sounds using solids like; ceilings, walls, and floors.
The transducer is approximately 4” in diameter and 1-1/2” in thick. t weighs approximately two pounds and the outer surface is plastic but not sufficiently durable to withstand routine submersion. So in Part 1 we show how to encase the transducer for submerged use. This can be done for the unit on the boat too, but it is not necessary, as the unit on the boat can simply be placed against the bottom of the hull.
The transducer has a nominal impedance of 8 ohms and requires approximately 5 watts of audio power to operate with a maximum 30 watts.
Once we had the ability to play music underwater from a submarine, the question became "What should we play?"
So here is our underwater play list.
Here David came in paid us a visit in Tulsa, and he, Kay and I (Doug) build one of David's HBH-2 Hydrophones.
David continues his step by step instructions for building his HBH-2 Hydrophone. This unit also makes a great underwater camera or light housing.
David completes the HBH-2 Hydrophone and we take it out to the lake for testing.
The solids transducer is rated of 30 watts and we tested to 180 feet with only 3 to 4 watts going to it. So if you want to hear further away, just TALK LOUDER!
Sometimes what you need comes ready made under a different skin. (1) This 50 watt bullhorn sells for less than $40 including shipping. I got mine off eBay, but you can get them from www.prohoists.com too. The small amplifier card uses 12 volt DC and the microphone is differential so it does not pick up background noise or wind. The rest you don't, need. You could but the parts separately and build it from scratch but you'll end up paying more, and spend hours doing it.
With this amplifier powering the same solids transducer used in the videos above, we were able to transmit 600 feet!
On the other side of the coin we found a way to listener better too. Changes to the hydrophone have made it more sensitive to lower frequencies so there is less interference from waves and boat, and it's easier and cheaper to build.
(5) (6) Yes, four 32mm piezo disk are better than one. It's more stable and better for lower frequencies which are away from the high frequency noise of props and waves. It also give you built in redundancy and you can customize it of the fly buy simply running each piezo through an independent switch. An 1 1/2 inch thick PVC ring cut from a 4 inch Sewer and Drain coupler will form the side of the housing. You drill and tap it for 1/4 inch treads and tread in a hose barb for 3/8 inch hose.
(7) Superglue the piezo disk to a 1/16 inch aluminum sheet. Solder each piezo to one twisted pair in a Cat-5 computer cable, and put a little Goop over the solder connection to insulate it.
(8) Run the Cat-5 cable through the hose barb and use more Goop to glue the coupler to the 7 x 7 inch sheet of aluminum.
(9) Bolt on another sheet of aluminum through holes in the corners with bolts that stick out an inch or so beyond the nut. Put shims on these bolts between the sheets or only finger tighten these.
(10) A 3/8 inch air line is slid over the Cat-5 cable and attached to the hose barb to make a water proof seal. The solids transducer is then bolted to a third sheet of aluminum that has 1/4 bolts taped and treaded through the corners. Then 1/4 inch air line is pressed over the bolts from both parts to join them together.
The hydrophone that will be used by the surface boat need to be
rugged but easy to deploy and recover. And it only needs to be water
proof to about 10 feet, so this is what we did.
We got in the hot tub with the unit tonight and it was surprisingly easy on the ears, even at full volume. And the quality was outstanding good for underwater. It sounded no worse that a department store or school PA system.
Getting the piezo to survive is really not much of a problem. At
shallow depths we tested a piezo enclosed in nothing more that
Plasti-Dip. If you mounted that to your boat on a piece of open
cell foam it would work well enough, it could even be under a
panel. Put four 32mm piezos in a cluster and the quality of the
signal goes up. I need to build a test chamber to see what they do
at depth, but I eventually want to use them at 3000 ft on an ROV.
That 20 watt solids transducer on it own is not going to do any better than 600ft but if we were to shift the frequency lower, and also add real-time filtering to eliminate the upper frequencies then we should be able to eliminate speed boats, waves, snapping shrimp, etc and hear the broadcast further.
Some good advice came from the Yahoo Group; micbuilders
"The most standard for voice channels like telephone is 300Hz to 3000Hz (3KHz). You need a high-pass (aka "low-cut") filter to eliminate the frequencies below the band of interest, and a low-pass (aka "high-cut") filter to get rid of the frequencies above the band of interest."
The off-the-shelf form for a frequency filter is an equalizer. So
I have ordered a couple of car equalizer amplifiers from
$15 each, including shipping.
Tim Smalley's suggestion for how to jack my MP3 player into the analog bullhorn circuit: "If you wire a jack between one of the leads on the bullhorn's volume control, you can use it as an input as long as you keep the iPod volume down and use the pot on the bullhorn to control the loudness. Just take one of the volume control leads and cut it. Wire each end to the leads on an iPod size input jack. Test before soldering - you might have to swap polarity."
Take a Cobra 19 DX IV 40-channel CB (Citizens Band) radio with PA (Public Address) and switch it to PA mode when underwater where the radio will not work anyway. When the microphone is activated the 4 to 5 watts output is sent run thought a Pyramid PB70 150 Watt Power Amplifier/Booster, and then out through two 8 ohm, 30 watt underwater transducer. When the microphone is not activated, then then and DPDT relay has the microphone circuit connected to a piezo hydrophone and the PA output connected to a Metra AT-350E 7 Band Equalizer / 100W Car Amplifier that is connected to an external speaker. The Equalizer allows you to select the frequency range best suited to listening to the other transmitters output.
Cobra 19 DX IV 40-channel CB radio $50
Pyramid PB70 150 Watt Power Amplifier/Booster $30
2 - Transducer Underwater 4" Speaker In wall 8ohm $60
Hydrophone Piezos and misc parts $15
Metra AT-350E 7 Band Equalizer / 100W Car Amplifier $15
DTDP relay and misc electronics $15
Antenna & Mount $45
Michael Chisena has been in the communications equipment business
for over 30 years and offers an improved system. This
setup offers a better chance of working, lower current draw, no heat
sinks and separation of RF source (CB Set) from the audio gizmos to
prevent a possible fatal RFI condition. Most automotive graphic EQ's
are line level devices, it would be a real bad idea to drive them
with any kind of power.
The Ramsey 20 watt amp has many of the same features as the 40 watt unit. I can't imagine you need that much audio in an enclosed space. The TR system will turn DC on and off to the various modules as required, or break the audio paths. The down side to this approach is only the additional cost for separate amplifiers. Thanks to Michael for the diagrams too.
Another of Michael's ideas. If you don't need a CB or VHS Radio with your underwater communication system you can sometimes find stand alone marine hailers. Some old, stand alone marine hailers use their speaker as a microphone when they are not broadcasting. If you can find one of those units then it is only a matter of adding a relay that switched from the hydrophone to the underwater speaker when the hand microphone's Push To Talk; PTT button is pushed.
More likely, what you will find when searching for Marine Hailers, is VHS marine radio that has a PA/Marine Hailer switch on it, just like many CB radios. Some output 20+ watts which which can drive the sound-star transducer that is designed for 5 to 30 watts a nominal impedance of 8 ohms. I got this unit off ebay for $25 including shipping.
We build a PCV housing for a common speaker and compensate the housing with oil so the speaker can be submerged as deep as you like. The housing is fine and the speaker sounds good but the volume level is only marginal..
How a solids transducer works and building a PVC housing for a common speaker
Completing the PVC housing and testing the speaker.
An underwater communications console complete with two passive hydrophones and a single voice transmitter: $245. The ability to talk sub to sub or sub to support vessel without first having to surface: Priceless
This is David's dream project which consumes much of his time and effort. Below is a step-by-step process on how to produce a broadband voice transmitter good down to beyond 500'. Including examples of consoles, a basic block diagram, the parts you will need to build your own and sources for those parts. Build in on your own will actually cost you less that $245. That is what it will cost if you get David to build one for you.
Once fully developed and properly deployed, this system should provide sub to sub, sub to surface support vessel, or support vessel to sub communications even when the sub is submerged. When achieved, this will improve safety and enhance the overall submarine experience.
(1) Frank D's console #1 (left) and Les's console #2 (under construction) were originally Sonic Wave Fathometers popular in the mid '80's prior to being reconfigured for our use. On both consoles #1 and #2, a power isolation switch and indicator were used for each amplification channel. Future consoles will utilize but one set for both channels.
(2) A more detailed view of the first underwater broadband voice communications console. With this unit, the hydrophone signal does not pass thru the handset and the handset is activated by a mode selector switch. (mid level on the left)
(3) An enclosure after removing all the old application
(4) A new front panel in place and the electronic cards being positioned for standoff installation and mounting. Panels of thin wood are used as an insulator on which all electronics are installed.
(5) Both amplification channels have both the preamplifier cards and 7 watt amplifier cards installed. Cards are now on stand offs.
(6) Massive amounts of space is available in the earlier units for upgrades and modifications. The voice transmitter can handle up to 30 watts of power. In the earliest units, only 2 watts RMS was being used. This extra room can contain larger transmitter electronics without the need to change enclosures.
(7)With the vast area within these units containing nothing but air, a reduction in the overall console size is a project currently in the works. Console #3 on the left uses but a single power isolation switch and indicator to control power to both amplification channels to help further simplify operations. The jack plug located below the cb handset plug allows for a hydrophone to make use the lower transmit channel to listen at the same time on both channels. This jack plug is always active or "on".
(8) This same enclosure following cleaning and painting. This enclosure was later used in the making of Dean Ackmans #5 console.
(9) And finally, this voice transmitter as shown with the other components that together allow this communications system to work. The hydrophone in the upper left jack-the headphones in the upper right jack-the handset in the lower left jack- and the broadband voice transmitter in the lower right jack.
(10) Once your message is sent, it will be up to the hydrophones and the upper listen channel to pick up and amplify the returning message. The selection between transmit and receive is automatically selected with the use of the CB styled handset on the newest models. This greatly enhances the units ease of use.
(11) This is the overall basic block diagram of the passive sonar/underwater communications console. Only the location and number of jack plugs and the location within this schematic of the protective fuses differ from one unit to another.
Step by Step
(1) This is the start of a sequential step by step process to make
a broadband voice transmitter.
(2) Find a suitable bit for the three stainless steel mounting bolts.
(3) Drill the three holes.
(4) Tighten these very tight to prevent leaks during molding plastic curing.
(5) Cut the top off of a gallon plastic container. This is what we will mix out two part molding plastic.
(6) Wipe the inside clean of left over trash.
(7) The two part molding plastic I used. (The two part molding rubber supplied could produce 8 to 10 hydrophones and this cost could be shared by 5 systems...( its about $55.00)
(8) Make a mark at both the full level and about half way down. This will be used to make two voice transmiters.
(9) Find a suitable drill bit for our interface cable.
(10) Drill this hole and install this.
(11) Prepare the white and black wires for use. (cut the green wire off)
(12) Upon inserting this cable into the "o" ring, install the crimp connections.
(13) Install these crimp connectors onto the transducer for solids.
(14) Before pouring the plastic, ensure this dish is level.
(15) Pour the plastic compound until you reach the 1/2 mark made earlier.
(16) Do the same with the second part of this mixture and mix this well in the gallon mixing container.
(17) Pour this mixed solution over the transducer for solids until this completely covers this transmitter and fills this dish.
(18) This stuff cures at 350 degrees so be careful not to get burned. Once fully cured, it turns almost pure white and gets very hard to the touch.
(19) Solder on the end plug on the interface cable end.
(20) Inspect your work. This of course lacks the required thru-hull connection.
(21) This shows console #5 being wired together. The upper or "a" channel is already finished.
This unit is destined for Dean Ackman.
(22) Another shot to show detail.
(23) And another to better show the controls and indicators.
(24) Console #5 is completed!
This console being so compact should be ideal for psub use aboard most smaller 1atm submarines such as the k250 and K350 submarines.
(25) Console #5 is completed!
This console being so compact should be ideal for psub use aboard most smaller 1atm submarines such as the k250 and k350 submarines.
(26) This shows the isolated power connections on the units back panel.
(27) The positioning of all of the enclosures controls and indicators are well planned and pleasing to the eye.
The upper or "a" channels two input jacks in the upper left, the gain and volume controls near the units center, and the output jack on the upper right. (like reading a page in a book!)
The lower or "b" channel are positioned identical and is used as the transmit electronics (although two hydrophone input jacks are also included so both channels can listen at the same time) This feature could aid in contact exact bearing determinations.
(28) Console #6 showing the pre-amplifier and amplifier cards for both channels installed. This console #6 is a sister to the above image of #5 in all respects.
Of note is the use of teflon white washers to isolate the jack plugs from the front metal panel as opposed to rubber washers. It was felt that rubber would not last as long as teflon.
(29) Another shot of console #6 showing the back of the control panel. No wire from these boards have thus far been installed.
Connecting all these wires will actually not take that long once these boards are put together and thus installed.
The inside of the outer cover has been etched with the number "6" along with my initials "D.P.B.".
(30) A completed unit has now been installed on Dean Ackman's sub.