How to Make a Contact Microphone

HELLO EVERYONE!!!!!!

Its been a while since I last posted an instructable and I just saw that we passed 200k Views!!

Well, to celebrate and help keep you busy while staying indoors due to the current pandemic (Stay safe), I've come up with a new instructable to share.

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Disclaimers: links for supplies are through amazon affiliates; as well as alternative links for those without Amazon, it gives me a little help if you purchase something through the link and also gives a little incentive to stay home rather than go out and buying the supplies during the pandemic.

I am not an electrician, therefore my word should not be taken as the absolute correct way to do things and you should always consult your own judgment when using soldering equipment and high voltage equipment. I cannot be held responsible for damages resulting from improper use or understanding of electrical equipment, you proceed at your own risk.

Piezo Sensors by their nature do not have very high fidelity and are meant to be paired with outside microphones. Placing the microphone in an enclosure or otherwise modifying the original sensor will change its resonant frequency. If you wish to have the highest fidelity possible, only apply the 5min. epoxy as seen in step 2.

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Information:

Piezoelectric Sensors: Piezoelectric sensors (Piezo Pickups) are used to record vibrations on surfaces. A Piezoelectric Sensor contains a Piezo Crystal which generates an electric charge when the crystal is deformed. the fact that it generates its own power makes it a "Passive" device which means that it does not need external power. Piezo Mics "Contact Microphones" are commonly used in Foley studios for a myriad of purposes.

3-pin XLR Cable: These are good cables to start with.

Amazon: ( https://amzn.to/2WpChy4 )

Alternative: (https://www.guitarcenter.com/search?Ntt=xlr)

Piezoelectric transducer: These are the ones I got.

Amazon: ( https://amzn.to/391M3sX )

Alternative: (https://tinyurl.com/vufz37m)

Soldering Iron: I got this little kit that comes with a little bit of everything.

Amazon: ( https://amzn.to/391M3sX )

Alternative: ( https://tinyurl.com/tre3jjf )

Heat shrink tubing: in. 3/8" - 3/16" mm. 9.5 - 4.7: I recommend this kit.

Amazon: ( https://amzn.to/391M3sX )

Alternative: ( https://tinyurl.com/y6b74ypb )

Lighter or Heat Gun: you can use either a lighter or the good old Black&Decker Heat Gun.

Amazon: ( https://amzn.to/3daEDa2 )

Alternative: ( https://tinyurl.com/vkxqbdp )

(Optional) 3D Printer: for creating the housing. I recommend the Ender 3 Pro.

Amazon: ( https://amzn.to/391M3sX )

Alternative: ( https://tinyurl.com/wx2ebwj )

(Optional) PLA Filament: Best filament for 3D printing I've used so far.

Amazon: ( https://amzn.to/391M3sX )

Alternative: ( https://tinyurl.com/rtdyaht )

(Optional) Liquid Rubber: Optional for sealing the Mic.

Amazon: ( https://amzn.to/391M3sX )

Alternative: ( https://tinyurl.com/tukq9qz )

5 Minute Expoxy: For Reinforcement and gluing.

Amazon: ( https://amzn.to/2QtlkPs )

Alternative: ( https://tinyurl.com/wtblcqr )

You can use several cords for this Project (Eg. 1/4 Cable, 3.5mm Cable, XLR Cable). I chose to use an XLR Cable as they have really good shielding and aren't as susceptible to breaking as the other choices.

Step One: What you want to do first is cut off the female end of the XLR Cable as this is where you will attach the Piezo Sensor. Once the cable is cut, use a pair of wire strippers or a knife and strip off a 1/2in. (12.7mm) section of cable

Step Two: Once the cable end is stipped, you should see the copper wire surrounding the inner cables, this is the cable shielding and can be gathered, twisted, and cut off as we do not need it for grounding on this side. Once the shielding is out of the way, there should be cloth and string also surrounding the inner cables, this can be gathered and cut off. now that you have everything out of the way, you can stip off a small section of wire from both the positive and negative wires.

Step Three: Now we can get out the solder and pre-solder the exposed wire at the end of our cable, this will ensure a strong connection later, as well as keeping the wire from fraying while we work. To do this just get your soldering iron heated up, and apply a small amount of solder to each wire and coat the exposed portions.

If you have a 3D printer or are otherwise wanting to use an enclosure, please skip the soldering portion as you will need to place the sensor in the housing before soldering

If you bought the Piezo Sensors I suggested, your sensors will be slightly smaller than the ones I am using in the demonstration. However, the steps are the same for any size Piezo. We also have a few methods of finishing the Contact mic which we will get to later.

Step One: Grab your Piezo Sensor and identify the Positive and Negative leads, if your Sensor does not have leads already, the white part is positive and the metal is negative. If your sensor does come with leads, go ahead and Pre-Solder them as you did in the previous step. Alternatively, if your sensor either does not have leads or you don't like the leads that come with the sensor, you can de-solder the current leads, and solder the wires from the XLR cable directly onto the Sensor, doing this will result in a better and stronger connection.

Step Two: If you are not using a housing, you can go ahead and slip-on 2 small sections of heat shrink tubing to the positive and negative wires, then solder the wires together (alternatively you can use electric tape to protect the connections). CONGRATULATIONS!! you just made a basic Contact Microphone, You can stop here if you want, however, there are a few options on making the Contact Microphone more ridged and last longer. Here are the Methods I recommend for finishing the Microphone:

Option 1: Electrical Tape and Epoxy; for this option, you basically just wrap the 2 cords together in electrical tape and add a small layer of Epoxy to the top of the Piezo Sensor to give it a protective ridged backing and you're ready to go! this will give you the highest fidelity

Option 2: Rubber Dip; for this option, you need to wrap the two cords in electrical tape, then dip the entire contact mic into the rubber, after dipping, place the contact mic metal side down onto wax paper to give the Mic a flat surface. once dry the mic is now waterproof and protected, however, this method will decrease the sensitivity of the contact mic a bit. Alternatively, you could also use Rubber spray to apply a thin coat to the sensor.

Option 3: 3D Printed housing (Next Step for more information)

Disclaimer: Using an enclosure will change the resonant frequency of the sensor and may make it less sensitive. Before Gluing, ensure the Piezo you chose is working correctly by connecting the leads to the XLR and doing a test recording.

For this project, I designed an enclosure for the contact microphone and modeled everything around an XLR cable and a Piezo disc less than 2 inches wide.

Step One: To print this part you will need the .STL file which I have provided. the file should have all of the measurements needed. my print settings are as follows:

• Layer height .1mm
• Speed 80mm/s
• infill 25% (Might sound better at 100% infill)
• no supports

Make sure that when you print, the top and bottom pieces are printed with the notch facing up.

Step Two: Before you start, I recommend De-Soldering any leads already attached to the Piezo Sensor, that way you can solder the wires from the XLR Cable directly. Once you have printed the enclosure, glue the middle section and bottom together, making sure to line up the hole points otherwise you won't be able to slide the cable in. Once the bottom and middle sections are glued, Glue the Piezo Sensor to the inside of the enclosure, do a test fit with the cable to make sure you have your wire at the right length, you may need to trim your wires to make everything fit right. When the Sensor is glued and the wire is at the right length, slide the exposed end of the XLR cable into the cable hole as shown in the pictures and solder your connections, remember, The metal on the sensor is negative and the white part is positive. When the soldering is done, you can now glue on the top portion of the enclosure. You're Done!!

Step Three: Record Something!!! I have provided a small audio sample of me using the Contact Mic. to make the sound of footsteps on a boardwalk.

Thank you for reading my instructable, enjoy your new Contact Microphone, there a lot of fun and have a multitude of possibilities.

If you have any questions, feel free to ask in the comments, I will try to respond to all of them as fast as possible.

Have a great day and stay safe!