The Legendary Blue Crystal Microphone




Introduction: The Legendary Blue Crystal Microphone

About: When I started my course in electronic, I dreamed of building audio gadget and synthesizer. Unfortunately, my course was a 'how to repair audio/visual equipment' type and not 'design cool stuff' type. Neverthe…

After reading a great comment to one of the most popular video of my channel, I got driven in one of the most positive way to push the limit of my knowledge and tackle my first ''Chemical'' project.

To make a short story out of a big story:

  1. I made a video on how to create a Piezo disk microphone years ago.
  2. It was basically just me showing how to solder 2 wires to a piezo disk element
  3. 2 years later, someone made a comment, you can read it here:
    So, you're another person NOT making a piezo mic, but repurposing an existing one. The closest I have found is the Colin's Lab where he grows piezo crystals. I can't find any videos of people actually making a piezo mic.
  4. Instead of bursting in tears or getting angry, I decided to accept the challenge
  5. I did my research and 2 weeks later, I had harvested my own Rochelle Salt Crystal...
  6. Another week later, I manage to 'manufacture' these crystal and create my own microphone with it.

Today, I present you the recipe of my hard work and also, the Legendary Blue Crystal Microphone.


To harvest the Rochelle Salt Crystal you will need the following. Fortunately, everything can be found at the grocery store, if you live in the same city I live, it is possible that the cream of tartar is out of stock, sorry! ;)

  • 250ml of Distilled Water

  • 150g of Cream of Tartar (Potassium bitartrate)

  • 500ml of Baking Soda (Sodium Bicarbonate)

To manufacture or house the Crystal and create a 'usable' microphone, you will need the following or so:

  • Patience
  • Dexterity
  • A small clamp
  • Epoxy or transparent silicon
  • Wires to connect to the mic

Step 1: Create the Sodium Carbonate

Wait, I thought you said Sodium Bicarbonate which is baking soda!

You will need to create Sodium Carbonate out of the Baking Soda which is Sodium Bicarbonate. Fortunately for us, the process is fairly simple, you only need to pour the Baking soda in a pot on the oven and put the heat to high.

Stir the powder until you see some bubbles, this is the CO2 and the water evaporating.

When there are no more bubbles, reduce heat and put aside.


If you don't feel comfortable with this process, watch that video since it was also my first time doing so and was fairly easy:

Step 2: Hot Bath

Pour 250ml of Distilled Water inside a Pyrex measuring cup and add 150g of Cream of Tartar. Prepare a hot bath with a pot and regular water (1/3 of the pot should do) and make sure the measurement cup will fit in there.

Stir the distilled water with the cream of tartar to ensure that it’s well mixed and put the measurement cup inside the hot bath. (Make sure it is not boiling but just near boiling)The goal here is to heat the solution as much as possible.

Step 3: Chemical Reaction

Take half of a tea spoon of your Sodium Carbonate and mix it with the solution which is getting hot. You will see a lot of bubbles forming, this is the chemical reaction and I hope your measuring cup is big enough, at least twice the size of your solution. (500ml is fine)

Progressively and slowly add the Sodium Carbonate to the mixture and wait between each reaction. Stir Often! When the solution gets from a milky tone to a clear yellowish tone, this mean that the solution is ready.

Step 4: Filtering

Add a last half tea spoon of Sodium Carbonate to make sure there is no more reaction in the solution. Crank the heat of the hot bath and make sure the solution comes to a point of ‘near’ boiling. Once it’s there, carefully remove from the hot bath (use oven glove or special tool) and make sure the solution doesn’t cool down as you will have to pour it inside a Coffee Filter and collect the liquid into another container.

The liquid is hot as well as the container so be really careful when manipulating it!

Note that this step is crucial. If the solution cools down before you filter it, most of the crystal will get stuck inside the coffee filter and your solution will be sterile, which means, No Crystal.

Step 5: Collecting the Liquid

Transfer this liquid into your desired container and put to the fridge.Within an hour or 2 you should start to see the formation of Crystals, If it’s not the case, something went wrong.

In my first attempt, I decided to experiment and add some food colorant to some compartment containing the solution. The result is amazing and I ended up with some purple, blue, red and green crystals.

Step 6: Testing Your Crystal

Unfortunately, some of your crystals may not be good candidate to become microphone. But, some of these crystal will react fairly well to vibration or impact.

This is time to test the microphone. You will need the following:

  • Aluminum foil paper or copper foil tape
  • A small clamp or plastic C-clamp
  • Some wires or alligator clip
  • An Oscilloscope

To see the process of testing the piezo, watch this video here, it will also gives you an idea of how to create the testing environment for such a device:

Step 7: Creating Your Legendary Microphone

According to this video, the process of making or housing the microphone was top secret.

Since this is an Instructable, I'll do my best to explain the process.

First of all, a single crystal will react to sound but during my experimentation, I notice that a stack of 2 Crystal could increase a lot the quality of the sound, the amount of gain as well as the frequency response.

This is most of the secret behind the Legendary Blue Crystal Microphone.

It is mostly a sandwich of crystal layered that way:

  1. Blue Crystal
  2. Aluminum Foil With the positive wire
  3. Another any color you like Crystal
  4. A piece of copper foil with the negative wire

Note that there is some annoying noise in this build, I think the mic should be shielded properly by adding more aluminum or conductive surface around the mic. Tho, I really wanted to leave the Blue Crystal exposed so people get to see the layer of the finish product.

This is why I highly encourage anyone to try and design their own Crystal Microphone, I'd like to hear how you build yours and how it sounds.

For additional documentation concerning Rochelle Salt Microphone, check this out:

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    8 months ago

    awesome job :) getting it to work is far from trivial, well done!
    good luck with your channel :)


    Reply 8 months ago

    Thank you for the kind comment. I really had a hard time making that small microphone work properly. When I want to criticize my work, I think that this microphone was once only water and powder, than it makes me smile.


    8 months ago

    Nice. Thanks for sharing.
    Simple and easy to follow.


    Reply 8 months ago

    Thanks for that comment, it motivate me to create much more Instructables. I really like the community here.


    8 months ago

    Nice. Thanks for sharing.
    Simple and easy to follow.