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Recorder | TASCAM | International Website

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TASCAM has developed a recording equipment and tools for music production for musicians and creators.

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Introduction: Make a Contact Microphone

A contact microphone is a type of microphone that picks up vibrations from contact with objects, as opposed the the more common type of microphone that picks up pressure waves in air. Here's a demo of a contact mic attached to an alarm clock, along with finger tapping on the table about a foot away from the clock:

In this Instructable, we show you how to construct a professional quality contact mic that is very rugged and sounds good. It has a 1/4" female jack so that you can connect it to an amplifier with a standard guitar cable.

This particular version of a contact microphone was designed for the premier of The Immortal Flux, a composition for drum kit and prepared drumhead orchestra written by Glenn Kotche, drummer for the band Wilco, at the Solid Sound Music Festival, sponsored by D'Addario.

To learn more about about the common ground between technology and percussion music, including tips on composing your own works from ensemble Third Coast Percussion, see this Instructable on the WAVES project.

Step 1: Parts and Tools

Parts

27mm diameter piezo bender, also known as a "buzzer element", such as this part from Digi-Key

8" length of 2-lead, shielded balanced microphone cable, such as Mogami W2582

1/4" inline female mono jack (sometime called TS or "tip-shield"), such as Rean/Neutrik NYS2202P

cap from 20 oz pop bottle

Tools

soldering iron and solder

wire strippers

flush cut wire cutters

1/4" and 5/16" heat shrink tubing

hot air gun or candle

hot glue gun

sandpaper

About Piezo Elements (Benders)
A piezo element is a metal disk with a circle of piezoelectric crystals in the middle. When the crystals are made to vibrate, they produce an oscillating voltage. Conversely, if you apply an oscillating voltage to a piezo element, it vibrates--that's why they also work as buzzer elements. A piezo element has 2 terminals: the inner circle which is the signal terminal and the metal disk which is ground. A good discussion of piezo elements and how they work can be found at Open Music Labs.
About Balanced Microphone Cables
Since a piezo has 2 terminals, we need a cable with 2 conductors to connect to it. You might think that simple speaker wire would do, but there's another consideration--cables can act as antennas that pick up stray electrical signals in the environment that can cause audible hum when plugged into an amp. To counteract this, you need to use shielded cables that have a sheath of wire surrounding the conductors. Shields are typically made of thin copper wire that is either wound in a spiral or braided around the conductors. (Foil shields are also used for cables that a part of permanent installations, but are not appropriate for this project.) Audio technicians typically agree that the highest quality (and most expensive) mic cables use braided shields, but spiral wound shields are perfectly fine for this project, and are somewhat easier to work with. In addition to the 2 conductors and the shield, mic cables may also have "filler" that helps the cable maintain its round shape. This filler may be plastic lines or bundles of thread, as pictured above. It doesn't matter which type you use for this project--if your cable has filler in it, you'll just need to snip it off before soldering your connections. You can buy bulk microphone cable from online suppliers such as Redco or Parts Express, or else you can just buy a mic cable from your local music store and just cut it. Do not use guitar cable for this project--it has a very different arrangement of a single conductor surrounded by a shield which is not appropriate for connecting to a contact mic in the manner we suggest.

Step 2: Strip Cable End for Jack

1. Start with an 8" length of mic cable.

2. Carefully strip around a half inch of the plastic or rubber cable housing from one end using a sharp hobby knife or an adjustable wire stripper. (Strip just enough to be able to make connections to the jack.) Be careful not to cut the wires or shield inside--just slowly score the housing until it splits and then pull it off.

3. Separate the copper shield wires into a bundle. If there is filler, snip it off (be careful not to cut the wires!)

4. In a typical mic cable, one of the insulated conductor wires is either blue or red and the other is clear. We'll use the clear wire as ground. Strip the ground wire down to as close to the edge of the cable housing as you can and twist the wire together with the shield.

5. Strip off around 1/8" inch from the end of the signal wire and twist it into a bundle.

6. Bend the stripped end of the signal wire 90 degrees, to create a little tab that we will insert into the signal terminal of the jack.

Step 3: Solder Leads to Jack

The jack has two terminals: a signal terminal that goes to the tip of a plug and a shield terminal that goes to the grounded plug housing and the cable shield. The signal terminal is usually a metal tab connected to the body of the jack with a small hole in it. Some jacks may have two signal tabs. If the jack is a mono jack, then you may connect the signal to either one of these. The shield terminal is usually a long strip of metal that may have a folded tab that forms a "pocket" for connecting the ground wires, or there may be a small hole in the bottom of the strip. The figure above is of the pocket variety.

If you plan to do a lot of soldering, it's worth investing in a good iron, as well as a good set of strippers and wire cutters. I use a temperature controlled iron set at 700 degrees with a chisel tip. This transfers a lot of heat quickly and melts the solder fast, which I prefer. There are a number of good Instructables on how to solder.

Before you connect the wire leads to the terminals of the jack, you should "tin" the wires by applying a small amount of solder to the wires. I use a cheap "helping hand" tool with alligator clips to hold my work while I solder.

After you've tinned the wires, put a small blob of solder in the "pocket" of the lead terminal. You should touch the soldering iron to the inside of the pocket to heat it up and then slowly feed the solder into the point where the tip of the iron and the pocket terminal meet.

Now we're ready to connect the wires. Fit the angled end of the signal wire through the hole in the signal terminal and solder it into place with a small amount of solder. Next, slide the ground wire up into the pocket and solder it into place. Use flush wire cutters to cut the wire ends off flush with the terminals. Using pliers, crimp the tabs on the end of the ground terminal to grab the cable housing. When you're done, it should look like this:

Note that there is little excess solder and there is clean separation between the signal and ground connections. It's worth taking your time to get a clean result.

Here's an example of a plug that has a small hole instead of a pocket for the ground wire. To connect the ground wire, simply bend it down to fit through the hole. Note that a large bundle of wire won't typically fit through the hole. To get a smaller bundle snip of half of the shield wire before you twist the shield to the ground lead wire.

Step 4: Heat Shrink Tubing Over Jack Connections

Heat shrink tubing over the jack connections serves 3 purposes:

It protects the signal connections from shorting to the grounded shield housing

It adds mechanical strength to the connection

It reinforces the place where the cable enters the jack, to keep it from breaking from too much flexing. (You know how annoying it is when the cord on your phone charger wears out at the joint!)

1. Cut a 2" length of 5/16" diameter heat shrink tubing and slide it over the jack terminals as shown

2. Turn the tubing slowly over a heat gun or candle until it shrinks

3. If the jack came with a plastic jacket, slide that over the shrunk tubing.

4. Screw on the housing.

Step 5: Prepare the Cable End for the Piezo

1. Strip off a length of cable housing that's the same as the diameter of the piezo, a little more than an inch.

2. Completely trim off the shield wires and any filler material

3. Strip 1/8" inch of insulation off the ground wire and fold it over 90 degrees

4. Trim the signal wire to a length near the middle of the inner circle crystal contact and strip off 1/8" of insculation

5. Tin the ends of the wires with solder--be generous with the amount of solder

6. Shrink on a short length of 1/4" diameter heat shrink tubing (around 3/8") over the cut end of the cable housing. This is to prevent any stray fringe wires ends from the copper shield from touching the the crystal contact when we solder the leads in place.

Step 6: Solder the Leads to the Piezo

1. Melt a small blob of solder near the perimeter of the metal ground disk. To do so, first hold the iron to the disk and then feed a little bit of solder to the point where the iron and the disk meet. Be careful no to let the solder short to the inner crystal circle.

2. Hold the end of the ground lead on the solder blob and touch the lead and the blob with the soldering iron until the solder melts and forms a joint.

3. Solder the signal lead to the crystal terminal. If the wire lead doesn't sit nicely against the terminal, it may help to melt a little blob of solder onto the crystal terminal like you did for ground, and then solder the lead to the blob.

Step 7: Test the Microphone

Plug the mic into an amp using a guitar cable. Test it by tapping on it.

Step 8: Mount in Bottle Cap

Cut a notch into a standard 20 oz drink bottle cap that is big enough for the cable to fit loosely. I do this by first drilling a 1/4" hole on a drill press (hold the cap with pliers or vice grips while drilling), cutting away the excess with wire clippers, and then using a Dremel or file to enlarge. Sand off the nubs from where the bottle cap attached to the ring on the bottle neck.

Apply hot glue over the solder joints and along the joint between the cable and piezo

Apply a generous ring of hot glue around the inside edge of the bottle cap. The glue should come right up to the rim of the cap. Watch your fingers--hot glue is hot!

Set the piezo and cable assembly into the bottle cap so that it is uniformly flush with the rim and hold in place until the glue is firm. It's important that you get it as close to flush as possible, so that the piezo will make good contact with a surface. Apply a ring of hot glue around the joint between the cap and the cable.

Dip the bottle cap and piezo into Plast-Dip just past the joint. Be sure to stir the Plasti-Dip well before you do the dipping! When you dip, lower the mic slowly (take a few seconds) and then remove slowly. Hang the mic by the jack, remove drips with a paper towel, and let dry for a few hours.

You're done!

Step 9: Compose and Play Some Music!

In this Instructable, Peter Martin of Third Coast Percussion provides tips on composing and playing percussion music.

Step 10: Using the Contact Mic As a Guitar Pickup

You can use this contact mic as a pickup for an acoustic instrument such as a guitar. If you do, you'll probably want to use a longer cable than 8", so that the jack clears the top. To attach the contact mic to the guitar, use a little bit of poster mounting putty. You can further secure the mic and cable using gaffer tape, which holds well but doesn't leave a residue when you remove it. You can experiment on where to place the mic to get the best sound, but just below the bridge on the side of the high strings works pretty well.

One issue with using a piezo contact mic as a guitar pickup, is that if you connect it directly to a typical guitar amplifier, some of the bass gets filtered out. Using a preamplifier with a high input impedance can correct this problem. I've written this Instructable on making a Guitar Contact Microphone Preamplifier as a solution to this problem. It's a simple design that fits inside of a mint tin, and also includes some basic explanation on how the preamplifier works.

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Make a Contact Microphone: A contact microphone is a type of microphone that picks up vibrations from contact with objects, as opposed the the more common type of microphone that picks up pressure waves in air. Here's a demo of a contact mic attached to an alarm clock, along...

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TO ORDER PLEASE VISIT THE ORDERING PAGE BY CLICKING HERE

C-SERIES+ CONTACT MICROPHONES

OCTOBER 2023

We're pleased to announce the release of the JrF c-series+ contact microphones, alongside some small batch versions in different colour combinations.

£45 (UK)
£50 (rest of world)

prices include standard p&p
(upgraded postage is available)

Supplied with 2m high quality, specifically designed cable & neutrik jack*
Extra cable is £3.50 per metre

The c-series contact microphones are already used by thousands of artists, recordists, sound designers and ecoacoustic researchers so we're keeping all the good things about that design. Indeed the hand built elements used for the c-series are as good as this technology can get, with the widest frequency range on the market & are also used in the c-series+ mics.

. thicker, oxygen free cable, with more core strands and increased flexibility.

. neutrik 1/4 inch jack as standard, with metal barrel, and brass one-piece connection
points to enhance signal transfer and reject moisture.

. extra layers of acoustic transfer and outer coatings to further protect the
microphone element
. smaller batches available in a in a range of colours.

. available in the classic black / white dot colour, or, in smaller batches, currently;

bark (brown / white dot)
cadmium (red / black dot)
cadmium ice (red / white dot)
obsidian (black / black dot)

c-series+ contact microphones can be ordered now.

when Pheobe started to collaborate on building JrF microphones she began thinking about colour, influenced by listening through the mics to trees, plants, insects (inc. ladybirds, hence the cadmium versions) and city surfaces.

the bark shifts, otter
salted
ladybird cadmium
obsidian

tilts metal resonant
foraging beneath the surfaces of
field, architecture, instrument or object

nb. if you already have the c-series contact microphones you don't need to upgrade, unless you want to of course. The differences, though beneficial, don't make the c-series obsolete, hence why they will continue to be available in the JrF range of specialist microphones. Both designs use the same elements & have a very similar frequency response.

****************************************************************************

C-SERIES PRO CONTACT MICROPHONES

prices include standard p&p
(upgraded postage is available)

Supplied with 2m high quality, specifically designed cable*

neutrik Jack upgrade £5 per microphone
Extra cable is £3.50 per metre

postage upgrades to first class, special delivery (UK) or fully tracked (EU / Rest of World) are also available

Supplied with 2m high quality, specifically designed cable* & a Rean brand jack as standard or ahigher specification metal barrelled Neutrik 1/4 jack with nickel or gold connection points (improving signal pass and condensation rejection) upgrade inc. postage is available for £5 per microphone.

Stereo pairs' are always two separate microphones, each with its own cable and jack. Therefore if you are ordering the jack upgrade remember that you need TWO for a stereo pair.please email me (using the contact form on the mail page) for quotes and estimated dispatch of custom length cabled units (nb. postage charges might increase if more than 5 extra metres is added to your order)

I do suggest using these microphones with the XLR impedance matching adaptors if your recorder has XLR inputs (see below), as this both improved the frequency response and also helps avoid interference from the recorder.

Extra cable can be added and on c-series microphones is currently £3.50 per metre.

NB. THE WHITE FOAM DOT IS THERE TO PROTECT THE MIC WHEN BEING PRESSED ONTO A SURFACE. IT IS THE OTHER 'NON WHITE DOT' SIDE THAT SHOULD BE PLACED ON THE SURFACE / OBJECT TO BE RECORDED

These are the highest specification contact microphones in the JrF range and widely regarded as the best contact microphones for creative recording / listening available.

Various unique processes mean that the c-series contact microphones provide a wider freq. response than others on the market - meaning more low end and mid frequency range response. They've also been designed without using toxic products, so you can use them out in the field without worrying about any environmental impact. A step up from the basic JrF contact microphone - features: High spec, low noise, flexible specially designed cable.*

Large diameter element providing, in conjunction with the JrF exclusive 'acoustic-transfer' coating, an even better signal and frequency response.

Strengthened top of element for increased placement and handling durability.

Available with 1/4 inch jacks (rean or neutrik) and with a range of adaptors to connect to XLR and 3.5mm inputs.

Available as single mono contact microphone or in stereo pairs.

NB. THE WHITE FOAM DOT IS TO PROTECT THE MIC WHEN BEING PRESSED ONTO A SURFACE. IT IS THE OTHER 'NON WHITE DOT' SIDE OF THE MIC THAT SHOULD BE PLACED ONTO THE SURFACE / OBJECT TO BE RECORDED

*there are significant supply chain and shipping issues globally currently, so there will be times where we use a different cable, of similar specification. This has been tested and the results are comparable.

here's a video of David Attenborough listening to a tree using a JrF c-series contact mic;

STANDARD CONTACT MICROPHONES

£25 (UK)
£28 (rest of world)

prices include standard p&p
(upgraded postage is available)

Supplied with 2m cable
Extra cable is £2.50 per metre

*postage upgrades to first class, special delivery (UK) or fully tracked (EU / Rest of World) are also availableAvailable with a Rean brand 1/4 inch or 3.5mm mini-jack (please specify) as standard.

please remember to add a note to your payment letting me know whether you want 3.5mm or 1/4 inch jack on your microphone.

I do suggest using these microphones with the XLR impedance matching adaptors if your recorder has XLR inputs (see below), as this both improved the frequency response and also helps avoid interference from the recorder.

Extra cable on standard units is currently £2.50 per metre.
Please email me (using the contact form on the main page) for quotes and estimated dispatch of custom length cabled units (nb. postage charges might increase if more than 5 extra metres is added to your order)

High quality hand finished piezo element.

Multi dipped in unique coatings.

2 metres of low noise, specially designed high quality cable.

Can be supplied with standard ¼ inch jacks or 3.5mm mini-jacks (please specify at time of purchase)

Adaptors to connect to XLR inputs and from two mics to a single 3.5mm input can be found on the ordering page

Ideal for use on instruments and in field recording.

**************************************************************************

*we have been asked for contact mics with magnets permanently attached, for affixing to metallic objects, structures, instruments and ground spikes, but there's a simple fact; they don't need to be permanently attached. They can be attached temporarily without any less connection strength, which also means they can be taken off again. This means the mics can be used in other ways where the magnet would either inhibit them being attached or where the thickness of the magnet would, in effect, damp the resonance. Additionally, the type of magnets usually needed for this, neodymium, can cause issues with hard drives & storage media, hence why it's best they are stored away from your recorder / laptops etc. Having them separate from the microphones makes this much easier.

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TO ORDER PLEASE VISIT THE ORDERING PAGE BY CLICKING HERE C-SERIES+ CONTACT MICROPHONES OCTOBER 2023 We're pleased to announce the release of the JrF c-series+ contact microphones, alongside some small batch versions in different colour combinations.

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Introduction: Electromagnetic Field Microphone

An electromagnetic microphone is an unconventional tool for sound designers, composers, hobbyists (or ghost hunters). It is a simple device that uses an induction coil to capture and convert Electro-Magnetic Fields (EMF) into audible sound. There are some commercial ones available, such as the Elektrosluch which is strong enough to capture ambient EMFs and some cheaper ones that need to be close enough to the source of the EMF.

This tutorial demonstrates how to make such a microphone, that captures the environmental EMF and converts it into audible sound by using an amplifier. It may not have the quality of an Elektrolusch but is still a fun project with which you can get some interesting sound effects (See videos in Step5).

The project is suitable for beginners. I made it having very little experience with circuitry and soldering myself.
Materials:

An old pair of headphones.

Enameled copper wire.

Headphone amplifier. I used the TDA1308 but you can try also with other models.

Battery holder. This depends on the amplifier you choose. If it is the model mentioned above, you are going to need a 6V holder. I recommend choosing one with an on/off button to make your life easier. Example here

Sandpaper or nail file.

4 x AA batteries

Tools:
Soldering Iron and solder wire.
Optional:

Access to a 3D-printer. This is to create a protective case for the copper wire. You can download a design here, but you need to edit the dimensions depending on the size of the copper wire holder.

Tube shrinkers to cover as much as possible of the naked wires. This will reduce unwanted noise significantly.

A 125*80*32mm case to put the amplifier and batteries in.

Glue gun.

Step 1: Prepare the Connections

Since the wire is enamelled, you will need to file the two ends using the sandpaper/nail file.

Next, you need to cut your old headphones.

You are going to need two pieces of cable: one that includes the phone jack on its one end and one bare cable.

You can use the sandpaper/nail file to get rid of the covering.

Step 2: Protecting Your Microphone (optional)

If you have purchased the optional case for the batteries and amplifiers, you need to drill two holes and squeeze the cables through them before you keep on with soldering.

If you haven't got a driller, like in my case, you can also try with a needle and a hammer. The plastic in these cases is usually thin and it should not take long to drill through.

Once you have drilled two holes, pass through the two cables from the previous steps.

Use the photo of the ready product as a guide.

Step 3: Solder the Connections

Follow the pictured schematic to solder the connections (obviously, designing is not one of my strengths...)

The red wire on headphones is usually for Right, the copper for Ground and a black, white or green for Left. If the headphones you used had a microphone, you will find an additional wire (just ignore this wire, no need to connect anywhere).

Don't worry which end to use between the copper wire for Left and Right, as it doesn't matter.

For the ground, you can either solder it along the Left wire or leave it unconnected.

If you don't want to follow the optional steps for housing, just add the 4 x AA batteries and you are ready to go!
You can connect the jack to any recorder or computer.

Step 4: Protecting Your Microphone (Optional)

If you have followed step 2, you should now have a similar result as in the picture.

Try to squeeze in the battery housing and the amplifier. You can use some glue to keep the batteries separated from the amplifier as in the picture.

For the copper wire, either use the 3D printed case or find a cap from a bottle that fits the enamelled copper wire.

You can use a glue gun to ensure the case won't come off, but also to make the microphone waterproof.

Close the case, connect the jack on a recorder and you are ready to go!

Step 5: Have Fun!

Once you connect your microphone to a recorder, turn on the battery power.

You should be able to hear your surrounding electromagnetic noise!
Note: If you are using headphones, please make sure to have turned down the volume of your recorder before wearing them as the noise from the microphone can become too loud and damage your hearing. Ideas:
Try to use your microphone close to electronic sources, such as washing machine, lights, computer, phone, wifi router.

Did you know that you can hear noises with an EMF microphone underwater? Check out the videos!
Digital Processing:
The captivating thing about recording EMF is that the frequency spectrum you will get is by far richer than the one you'll get from a normal microphone (check the attached spectrogram).

This means that you can use extreme pitch shifts and get results that sound completely different from your original recordings.

Check out an example of some extreme pitch-shifted emf recordings on the attached .wav files, with which you can make music!

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Electromagnetic Field Microphone: An electromagnetic microphone is an unconventional tool for sound designers, composers, hobbyists (or ghost hunters). It is a simple device that uses an induction coil to capture and convert Electro-Magnetic Fields (EMF) into audible sound. There ar...

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TO ORDER PLEASE VISIT THE ORDERING PAGE BY CLICKING

COIL PICK-UP'S
FOR ELECTROMAGNETIC RECORDING

£15 / £18 (UK)
£18 / £20 (rest of world)

prices include standard p&p
(upgraded postage is available)

*postage upgrades to first class, special delivery (UK) or fully tracked (EU / Rest of World) are also available

supplied with pre-mounted 1m cable and with 3.5mm or 1/4* inch jack

for picking up electronic signals / sounds ie. the internal sounds of a laptop, lightbulbs, recorders, household gadgets etc etc.

A fascinating and rewarding method used by myself in performance, installation and on several releases, also used by sound artists and field recordists around the world.

you can hear some of the sounds these can pick up on an exclusive MP3 track I created for THE WIRE magazine by clicking here. On this piece you will hear field recordings of the general wire office ambience along with the inner sounds of their computer systems, alarm boxes and light fittings.

Whilst some other coils on the open market have certain limitations placed upon them, these adapted coils can detect a wider range of sounds that the technology is capable of.

They come pre-fitted with a 3.5mm jack plug and can be used with decent 3.5mm to 1/4 inch or XLR adaptors.

PLEASE NOTE: I only adapt these coils - hence the price. Depending on which country you're in it might be possible for you to find coils that don't have the limiters on sale elsewhere.

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TO ORDER PLEASE VISIT THE ORDERING PAGE BY CLICKING COIL PICK-UP'SFOR ELECTROMAGNETIC RECORDING £15 / £18 (UK)£18 / £20 (rest of world) prices include standard p&p (upgraded postage is available) *postage upgrades to first class, special delivery (UK) or fully tracked (EU / Rest of World) are also available supplied with pre-mounted 1m cable and with 3.5mm or 1/4* inch jack for picking up electronic signals / sounds ie.

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Introduction: Let's Build Some World Class Hydrophones

Updated September 2022: SEE STEP FIVE FOR ADDITIONAL INFO

New Audio Demo Too!
Thomas Rex Beverly, a professional sound recordist, took a pair of these to Greenland in July. He released a commercial sound library using them. I put a link to the demo of the library at the end of this Instructable.

1. The right transducer

2. A high impedance, low noise buffer amplifier PCB Here: https://www.jlielectronics.com/diy-accessories/p4...

3. Resin to embed items one and two in

I spent 20 years in the Navy as a Submariner. Although I wasn't a Sonar Tech, I spent a lot of time in the Sonar Shack listening. You could hear all sorts of things; whales, crustaceans, pile drivers building north atlantic oil rigs, and of course, the occasional Russian Submarine. Being the Audio Guy I am, I found this fascinating and always wanted my own set of hydrophones to continue the journey. Which leads us to today's Instructable: Build your own professional grade hydrophones. These may not match the durability of what the Navy and commercial ones do, but they certainly meet or exceed the acoustic properties they do. Best of all, they are inexpensive to build.

1. Male XLR jack

2. Microphone cable (that can be submerged)

3. A mold to put the parts in - I have a couple ways to do this.

We need three critical things for the acoustics:

Other items for the build:

Supplies

Step 1: Background

What is a Piezoelectric material anyway? The phenomenon was discovered by two french physicists (Yea, Go Physics!) Pierre and Jacques Curie in 1880. In essence, applying a force to some crystal structures, causes a voltage to be generated. The converse is also true, if you apply a voltage to the crystal it will deform. Like most discoveries back then, it was hard to turn the concept into useful things. Then in World War I, the need to find submarines became important, leading to the invention of Sonar in 1917. Of course we kept improving that over the years, leading to the modern submarine sonar systems on my three boats. Interestingly, the basic transducer designs didn't really change. The most common material today for the transducers is PZT or Lead Zirconium Titanate. It is used for ultrasound, sonars, fish finders and all sorts of other fun things.

It was so important to the Navy they wrote a standard for it: https://quicksearch.dla.mil/qsDocDetails.aspx?ide...

The cool thing for us is that you can buy single quantities of already prepared PZT material in various shapes, already silver plated on two sides, just waiting to be turned into a hydrophone. All we have to do is solder on some leads! The shape that ended up using and sounded the best to me was the cylinder, same as the NOAA article. There is far more to this and for a lot more theory read this for background.
https://www.americanpiezo.com/knowledge-center/pie...
Then there is this amazing paper from the Naval Postgraduate school
https://apps.dtic.mil/sti/pdfs/AD1068326.pdf
Before we talk about the embedding of the transducer into urethane, a review of underwater acoustics is in order. Sound behaves differently in water than in air. Water is a liquid and non compressible. We tend to think of sound being 20-20,000Hz in air. That is because that is what we can hear. Bats and other nocturnal critters can extend that into the 100Khz plus range, which they mostly use for echolocation. In the water, sound waves go from about 10Hz to 1Mhz. Yup, one megahertz. That is mainly for imaging and advanced sonar applications. Above that, sound gets absorbed quickly. It also travels much further in water. And when you are in the open ocean, lower frequency sounds can travel really far. The other thing about bodies of water is reflections at the surface and the bottom. Lakes and the ocean are like gigantic caverns with lots of echo and reverberant properties.

The other difference between air and water is "speed of sound". In water, it is totally dependent on density. Which for the Navy and sonar, makes salinity, depth, and temperature really important. For example it is 1450 Meters per second in freshwater and 1500 Meters per second in salt water. In air it is about 345 Meters per second. Pay attention -- there is a quiz... For us we can ball park it 4.25 times faster. The reason I point this out is well, if we are going to record underwater sounds, we might as well do it in Stereo. So we should multiply the standard spacings for microphones by that amount to get a decent sound. Our ears are about 20cm apart or 7-8 inches, we should space the hydrophones at least 3 feet apart. For those of you with the calculators out... I am winging it. :-)

The last thing to take into account is how sound transfers from water to other things. This one can get complex. Sound is traveling in water as a wave. Changes in density cause a change in the speed and reflect or refract it. So, if we keep the resin we are molding the piezo element in as close to the density of water as we can, we will get maximum sound transfer without worrying about how the shape of the mold modifies the sound. That eases mold design.

Step 2: The Transducer

The most critical component to these is the actual piezo element we are using. I found one that works really well and is less than $20 each. What I found doing my research was that there are two types of transducers used, which also matches my Navy experience. The first is the Active transmitter. Think underwater speaker. The second kind, and what we are doing, is called Passive. Think underwater microphone. In my search I found a great article from NOAA This one showed the basics. I could not find the specific transducer they were using, but I found a company called Steminc, which has a plethora of them! I tried several which all worked, but this one, which is cylindrical, is the one I settled on.

Step 3: The Electronics for the Buffer:

After building many microphones with an Op Amp as the impedance converter, I smiled when I saw what they were doing in the NOAA article. They used a great one, but it was at EOL or "End Of Life". It only made sense for me to adapt my circuit for use in a hydrophone. Piezo elements need a high impedance circuit to pick up the voltage they produce. This is similar to a condenser microphone. One of the problems with piezo elements, and this applies to pickups on musical instruments, is that they need a high impedance preamp on them. We need about a 1Meg input impedance vs the 1Gig that a condenser needs. This has to do with the inherent capacitance of the transducer. The piezo element is 6600pf. So with a 1 meg resistor we have a low cutoff frequency of 24hz. This works really well. If it goes into a preamp with an input impedance of say 10K Ohm, (typical of line level inputs) it has a cutoff of about 2.2Khz. Which will sound really tiny and bad. Thus piezo pickups have a bad reputation. For those thinking ahead already, this circuit makes a fantastic pick up interface that runs off of phantom power.

This uses the same Opamp as in my Condenser Microphone instructables.
https://www.instructables.com/OPA-Based-Alice-Mic... https://www.instructables.com/True-Condenser-OPA-M...
In fact we are using almost the exact same circuit. The board is smaller 26mmX29MM to allow embedding into resin. And a couple components (the capacitors) are smaller in value but provide excellent results.

Here is how it works:

The Blue section has our two incoming 47Ohm resistors coupled into two 22uF capacitors. This passes the signal out to the XLR connector and the mic preamp. Tapping off of this are two 2.2K resistors. These feed the incoming phantom power to the Green section. The Green section has a 12V zener and associated resistors and capacitors which generate filtered 12VDC. Then in the Pink section, we have a resistor divider with two 47K resistors and a filter capacitor. This generates a stable voltage that is roughly half the 12 volts. We are using this as a "virtual ground" for the operational amplifier in the Red section. There are two op amp stages. One is a non-inverting buffer connected directly to the Piezo element with a 1M resistor connected to the virtual ground from the Pink section. The Yellow section are filter caps for the op amp. The .1uF should be as close to the supply pins as possible.

The op amp is the heart of the circuit. The OPA1642 has really low noise, low distortion, and high bandwidth. That gives us a flat buffer amplifier, probably good to a megahertz. Then we have an inverting buffer from the second op amp stage and its two 2.2K resistors. This lets us drive a differential signal into the mic preamp. All in a little 26mm X 29mm PCB.

You can order the board from PCBWay if you want to assemble it using Surface Mount Components, or you can order one premade and populated from JLI Electronics. I recommend that.

PCBWay: https://www.pcbway.com/project/shareproject/OPAAli...

JLI Electronics: https://www.jlielectronics.com/diy-accessories/p48...

Step 4: The Resin and the Mold

I tried to find the exact urethane resin that the NOAA paper used but couldn't. What I did find was perfect as it has a specific gravity, (which is related to water density pure water = 1) of 1.05 which is really close. And, the specific gravity of seawater is 1.03 so it is even closer to the seawater.

We are using this: https://www.amazon.com/gp/product/B00E3ZJ9XW/

It is easy to work with and most importantly, it has a Specific Gravity of 1.05 g/cc or almost identical of water. This is really important for sound transfer. Just like glass in water. The closer to the index of refraction for water that the glass is, the harder it is to see when it is submerged. For comparison, Water is 1.33 and glass about 1.5 so that is about a 10-12% difference. Acoustically this resin has a 3-4% difference making it quite transparent to underwater sound.

Step 5: Connecting It All Up

NOTE: For 60hz Hum I am adding a Ground Wire to be in contact with the water!
See the photos with the solid copper wire connected to the shield. This was added September 2022 due to feedback from several builders who experienced this. Doing some more research there are commercial ones that have a metal portion that is grounded and I found another The ground wire does not have to be long. Just that is is contact with the water the hydrophone is used with. NOAA guide from 2013 that recommends this as well.
Wiring the Piezo Elements

These are made from ceramic piezo material. It has silver plating on the inside and outside surfaces which can be soldered with some caution. PZT material has something called a "Curie Temperature" Normally that is associated with magnets. As in if you heat it above the curie temperature, it is no longer a magnet... For piezoelectric material, it means that above that temperature, it affects the piezoelectric properties. Which we want to avoid. Also, it is ceramic so heating it unevenly will cause stress and potential breakage. With that said, just be careful and watch the video. It is easy but be careful.

To maintain the polarity the same for the two transducers, we need to wire them the same. I chose to wire the Signal lead to the outside and shield or ground to the middle.

I chose this particular microphone cable for its durability, strength and ease of working with it. Note, there is "Waterproof" microphone cabling available. That is really for permanent installations where the cable is submerged for years. And it is priced accordingly. I have tested the fully built hydrophones for 24hours in my swimming pool with no issues.

Wire the PCB end mic cable per the picture and the video

The XLR connector end is standard Pin one shield, Pin two (hot) to blue and Pin three (cold) to clear.

IMPORTANT! After you solder the cable to the PCB and XLR connector, TEST IT BEFORE MOLDING!!!!

Step 6: Embedding the Assembly

My initial prototype was with two 50Ml measuring cups. I cut the bottom off of one and then glued it with hot glue upside down to the other one. Use enough hot glue to seal them together. A small bead the whole way around is recommended. There is no acoustic difference in the final build. We are using a two part resin. You mix equal parts "A" and "B" then stir it up. Couple things to note. The resin gets just a bit thinner (less viscous) as it mixes and blends. It gets a little clearer at that point too, That is about a minute of mixing. This is when it is ready to pour. Over the next few minutes it starts to set and gets thicker. About five minutes later, it turns white as it sets and hardens. In another 15-20 minutes, it is set hard enough to break the mold away. I used a single edge razor blade to score the mold on one side and then break it free. I did not use a release agent on the mold. This resin is pretty forgiving that way. One final note on the resin. You will see bubbles as it mixes and you pour. They do not affect the sound quality at all.

Before pouring the resin in, make sure the PCB and piezo element are not touching the wall or bottom. That ensures everything is sealed.
Note: The resin I am using worked for me without a Release Agent. You SHOULD use a release agent with any other kind of resin.

Step 7: Testing and Use

These are quite amazing! The circuit I am using gives about 100dB of dynamic range and between the cylinder and the circuit the frequency response extends to several hundred kilohertz. Along with capturing biologics, which I plan on when I can travel again, you can use them to record sounds that can be slowed down significantly to produce really amazing surreal soundscapes. These are a sound designer's dream. To do so, record with them at a high sample rate like 192Khz. I'm using a Zoom F6. Bring the file into any editor (Audacity is a great one for this) then slow it down 4-8 times. The above graph shows the sonic profile of the hot metal into water. Recorded at 192Khz into the Zoom the I plotted a 2-3 second snippet. See my demo at the end of the build video for this.

Here is the Demo of them used off the coast of Greenland July 2022 Soundcloud Demo:

Here they are in Dry Ice and Red Hot Metal

They are a great addition to your sonic arsenal. Enjoy! Please comment, ask questions and let us know if you build a set.

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Let's Build Some World Class Hydrophones

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Let's Build Some World Class Hydrophones: Updated September 2022: SEE STEP FIVE FOR ADDITIONAL INFO New Audio Demo Too! Thomas Rex Beverly, a professional sound recordist, took a pair of these to Greenland in July. He released a commercial sound library using them. I put a link to the demo ...

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TO ORDER PLEASE VISIT THE ORDERING PAGE BY CLICKING HERE

D-SERIES HYDROPHONES

£60 (UK)
£65 (rest of world)

prices include standard p&p
(upgraded postage is available)

Jack upgrade £5 per microphone

Supplied with 5m high quality, specifically designed cable*

Extra cable is £3.50 per metre

postage upgrades to first class, special delivery (UK) or fully tracked (EU / Rest of World) are also available

Supplied with 5m high quality, specifically designed cable* & a Rean brand jack as standard or ahigher specification metal barrelled Neutrik 1/4 jack with nickel or gold connection points (improving signal pass and condensation rejection) upgrade inc. postage is available for £5 per microphone.

Stereo pairs' are always two separate microphones, each with its own cable and jack. Therefore if you are ordering the jack upgrade remember that you need TWO for a stereo pair.please email me (using the contact form on the main page) for quotes and estimated dispatch of custom length cabled units (nb. postage charges might increase if more than 5 extra metres is added to your order)A step up from the basic JrF hydrophones - features:

I do suggest using these microphones with the XLR impedance matching adaptors if your recorder has XLR inputs (see below), as this both improved the frequency response and also helps avoid interference from the recorder.

Higher spec, low noise, flexible specially designed cable

Small profile capsule

Weighted to submerge to any depth needed

Higher specification element using a new 'ceramic weld' technique

Additional layer of the JrF exclusive 'acoustic transfer' coating

Quality 1/4 inch jack (Rean / Neutrik).

Available as single mono hydrophone or in stereo pairs.

*there are significant supply chain and shipping issues globally currently, so there will be times where we use a different cable, of similar specification. This has been tested and the results are comparable.

Extra cable can be added and on d-series microphones is currently £3.50 per metre.

STANDARD HYDROPHONE

£50 (UK)
£55 (rest of world)

prices include standard p&p
(upgraded postage is available)

Supplied with 5m cable
Extra cable is £2.50 per metre

*postage upgrades to first class, special delivery (UK) or fully tracked (EU / Rest of World) are also available Available with a Rean brand 1/4 inch or 3.5mm mini-jack (please specify) as standard.

please remember to add a note to your payment letting me know whether you want 3.5mm or 1/4 inch jack on your microphone.

I do suggest using these microphones with the XLR impedance matching adaptors if your recorder has XLR inputs (see below), as this both improved the frequency response and also helps avoid interference from the recorder.

Extra cable on standard units is currently £2.50 per metre. Please email me (using the contact form on the main page) for quotes and estimated dispatch of custom length cabled units (nb. postage charges might increase if more than 5 extra metres is added to your order)

As an experienced field recordist / artist / composer I have used this design to make recordings, in gallery installations and when performing live.

They come sealed and multi-coated (including unique marine and acoustic transfer coatings) + internally coated to provide a totally waterproof finish and are weighted.

They are available with either a standard jack or a mini-jack (please specify which you require at the time of purchase)

Adaptors for connection to XLR imputs and from a stereo pair to a single mini jack input can be found on the main page.

They come with 5m of cable as standard and extra cable @ £2.50 per metre can be purchased when ordering.

Pairs (for stereo) are also available.

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TO ORDER PLEASE VISIT THE ORDERING PAGE BY CLICKING HERE D-SERIES HYDROPHONES £60 (UK) £65 (rest of world) prices include standard p&p (upgraded postage is available) Jack upgrade £5 per microphone Supplied with 5m high quality, specifically designed cable* Extra cable is £3.50 per metre postage upgrades to first class,

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