Working Microphone From Trash

This isn’t another misleading clickbait tutorial, this is a genuine step by step guide to make a humble, yet great sounding microphone that can be used in a variety of applications. Don’t be disillusioned, this microphone will not replace professional studio microphones, but they are robust, reliable, and recyclable. The price tag associated with the construction of this microphone is also not clickbait, ALL the materials needed to construct this microphone can be found for FREE.

(The tools used throughout, however, do have an associated cost. Don’t be discouraged by this, simply find alternative methods to achieve the same results. Get creative! )

What you’ll need to recreate this project:

A piece of PETE 1 or PET 1 plastic (thoroughly washed )

A tin can with a ROLLED lip on both ends (also thoroughly washed )

An audio jack of some sort (1/4’’, 1/8’’, RCA, XLR )

A switch of some sort (optional )

A length of wire (preferably two different colours )

• The tin can and PETE 1 plastic can be found in your recyclables (technically not entirely free so my suggestion is to source them instead from your neighbours…).

• When sourcing the tin can, look for one that has a ROLLED or FOLDED rim (first image ) on both ends rather than a seamless bottom (second image )

• Your best bet for the audio jack, switch and lengths of wire would be to salvage them from an old radio or tape recorder. Basically, any sound or music related device is a good place to search for these parts.

• The piezoelectric element can be a bit trickier to source, but they are still prevalent in consumer products that *beep* such as microwaves, alarms, buzzers, children’s toys, etc.

*Be sure to read and heed all warnings before dissembling anything you are unfamiliar with !

So, Mr. Ham, how are we turning a pile of recyclables and some salvaged electronic bits into a functioning microphone? PLASTIC! Let me explain. Membranophones, a family of instruments with membranes such as drums, produce sound via a vibrating membrane that pushes air in waves which crash onto the beaches of our ears.

Our microphone will work identically, but in a completely opposite way. Let me explain further. When a person or instrument produces sound, air is displaced in audible waves stemming from vibrating vocal folds, strings, membranes, reeds, lips, etc. Those sound waves of air will crash onto a thin plastic membrane stretched over one of the ends of the tin can and cause it to vibrate.

We will capture those vibrations and transform them into an electrical signal that can be amplified by attaching the salvaged piezoelectric element to the membrane. Piezo elements (or transducers ) translate minute movements into minuscule electrical pulses which can be amplified into usable audio signals and can then be projected through loud speakers.

How will we be making this thin plastic membrane to catch the vibrations of everything that we want to record? I’m glad you asked. Onto the next step!

To produce our membrane, we are on the hunt for the extremely versatile thermoplastic –Polyethylene terephthalate. This plastic sounds exotic but makes up roughly 60% or more of consumer plastics, so there’s a good chance that you’ll find something made from it in your (or your neighbour’s) recycling bin!

It’s the type of plastic used for beverage bottles, polyester, carpets, mylar, as well as countless other food storage applications, and can be easily identified by it’s recycling symbol: PETE 1 or PET 1. I’ll be using an empty juice container for my microphone. I implore you to recycle the offcuts as it’s virtually the most recyclable plastic that is produced.

In this step, we’ll be exploiting the thermodynamic properties of that not so exotic plastic to produce a durable yet sensitive plastic membrane.

*Peppered throughout this Instructable are tips and tricks to help you make the process efficacious and safer, based on my personal experience. If you’ve found a better way to do anything mentioned, please don’t hesitate to share it so we can all learn!

Tip for cutting up PETE 1 plastic bottles:

Clamp a razor blade in a vise at a 45° angle so that only a ¼ of an inch sticks out proud of the jaws of the vise. Then, by holding the bottle by both ends horizontally, pierce the flat center section of the bottle by applying firm pressure against the blade. ½” Once the bottle has been pierced, spin it to cut the length of its circumference. After you succeed at cutting the bottle into two pieces, use scissors to cut perpendicularly to your initial cut and proceed to cut the middle section of the bottle into a useable sheet of plastic.

After cutting out a useable sheet from the PETE 1 plastic container that you are using, draw or trace a circle that is a 1/4 inch in diameter larger than the tin can that you are using. This can be a rough eyeballed estimate.

*Refrain from using a compass directly on the plastic sheet as you want to avoid piercing the plastic if possible. Instead, use the compass to draw an appropriately sized circle onto a piece of thick cardstock or corrugated cardboard, cut the cardstock/cardboard circle out and use it to trace a circle onto the plastic sheet. Another alternative is to find a round object that is relatively close in diameter to your desired size and use it to trace a circle onto the plastic sheet.

Now for the magic bit.

After thoroughly washing out the tin can, remove the unopened end of the tin can with a can opener. Then drill two holes into the side of the can at 90 degrees from one another about mid-way up the can. I used a stepped bit to do this and clamped my can in a vise to secure it in place while I drilled the holes. One of the hole's diameter must be large enough to accommodate the jack you are using and the other hole large enough for the switch you are using.

The next step is the trickiest bit of this build, but this simple ''jig'' should make things a bit easier. Cut a scrap bit of thin, heat resistant-ish material to roughly 12'' x 12''. Next, place your PETE 1 plastic disc (as close to centered as possible ), followed by your tin can, followed by another scrap piece of anything large enough to span the diameter of the tin can, and finally a weight of some kind (I’ll be using a Ham-mer ). This setup should allow you to spin the tin can and PETE 1 plastic disc with little resistance, you'll see why this will come in handy during the next step!

Now for the tricky bit. Move your setup to a well-ventilated area, outside is always best and start by holding one of the corners of your Somewhat Productive Susan Base so that it faces you.

With a heat gun (or blowtorch), apply steady heat just above the rim of the tin can, kissing also the surplus plastic until it curls and starts to wrap around the rim. Once the plastic starts to curl around the rim, spin the base of your setup so that the plastic curls up around the entire circumference of the rim of the tin can. Avoid staying in a single area with the heat gun for too long.

*But how long is too long? If the plastic starts to discolour by turning an opaque brown or yellowish colour or small bubbles appear in the plastic, then the area was heated for too long.

Continue heating and spinning until the plastic hugs the rim of the tin can tightly and the excess above the rim is undulated evenly. Let everything cool for at least 5-10 minutes then remove the tin can from the jig. Flip over the tin can so that the plastic membrane is facing up. Upon flipping over the can, you might notice that the surface of the membrane is a bit wrinkly. To tighten it up, apply a gentle even heat with the heat gun over the surface of the membrane, moving the heat gun side to side constantly until the wrinkles disappear. After allowing the plastic membrane to cool for a few more minutes, check that it is tight by rapping it with the eraser end of a pencil, it should sound like a tuned drum.

The 0$ microphone relies on simple electronics to function. To make the process painless, I’ve provided a visual wiring diagram.

I’ll be using thin gauge solid core wire for the wiring in this project. I’ve had better luck over the years with solid core wire when soldering to piezo elements as the soldering iron’s contact with the piezo element is kept brief. Using an old microphone cable for this project wouldn’t be a bad idea either as its shielded!

When soldering to a piezo element I always suggest using a heatsink to avoid damaging the fragile element, especially if it's your first time. If you do not have a heat sink, any thick piece of metal in conjunction with solid core wire and brief contact with the soldering iron should provide the piezo element with enough protection against overheating. I’ve also soldered to them without any heatsink of any kind successfully, so don’t fret.

Another thing you can do to make the piezo element more robust is to add some hot glue to the connection points.

After everything is wired up, TEST YOUR CIRCUIT. Do this before installing everything. After testing that your circuit works as it should, simply glue the piezo element to the inside of the membrane using a dab of hot glue or 5-minute epoxy. Then install the audio jack and switch into the holes we pre-drilled earlier.

Your $0 microphone is now ready for your next gig or recording session! Simply plug it into an amp or P.A. and turn it on! You will be impressed by the sound and will find plenty of uses for it either in the studio or live. One cool trick is to hold it by the cable and swing it in front of the speaker of an amplifier to get cool feedback effects!

Also, the condensation that builds up on the inside of the membrane doesn't seem to have any advert effect on the sound of the microphone. This is also a great kick drum microphone and in fact you can even use it as a percussion instrument!

But Mr. Ham is it robust enough to gig with? ABSOLUTELY! I've had the one illustrated (green membrane) for close to 10 years and it has always worked perfectly.

Want to hear it in action? Check out this improvised vocal riff I've entitled ''Quarantine'', enjoy!

Rock on!

Mr. Ham