Introduction: Easy Chladni Plate

About: By day I'm the lead developer of Starfish ETL and I perform CRM data integrations. By night I enjoy building things - robotics, my home theater, flying quadcopters and finding other geeky things to do.

This build began as a science project with my son. He wanted to do a project about sound - after some research we found this mesmerizing video that introduced us to Chladni plates. We were fascinated & knew we had to build one! Unfortunately that video give no real information about the device they use.

There were a few places online that we found instructions on how to build a Chladni plates. In particular there is this Make article Chladni Plate: Visualize beautiful acoustics and another instructable here Mechanical Wave Driver for Chladni Plate.

I borrowed heavily from these two projects in terms of the configuration. However my version differs from those because it uses a standard, unmodified speaker - greatly simplifying the project. These other versions involve modifying your speaker to make a "wave driver". Well, one ruined speaker and failed attempt later we were determined to figure out a way to use just a regular speaker (in my case I used a subwoofer). The driver method just seemed very complicated - I never quite figured it out.. all we're trying to do here is vibrate the metal plate, it can't be that difficult right? Well it did take a bit of experimentation but I think we ended up with something worked really well, all things considered. It was at least good enough for my son to get an A on his project and take first place in the Science Fair!

Step 1: Gather Your Materials

For this project you'll need the following items:

  1. A large speaker
    I used an old 8" subwoofer - a standard speaker may also work but you'll probably end up needing to use higher frequencies than I used.
  2. A computer to generate frequencies
    I used this free website - Online Tone Generator
  3. An amplifier
    Any amplifier will do - you just need something that'll boost the audio signal from your computer to power the large speaker. I used a guitar amplifier. It has a feature to take an aux-in and it worked perfectly. You may also need a 3.5mm audio cable to connect the two together.
  4. Sheet Metal
    Mine is an 18" square. I had to cut it down to this size. The only sizes I could find at the hardware stores were 12" which would have been too small, or 24" which would have just been too heavy. Make sure the gauge steel is sturdy enough to stay straight when horizontal - you don't want it to sag or all the salt will simply fall off your plate.
  5. Acrylic Sheet
    Usually called plexiglass, you'll have to cut this down to the correct size
  6. Threaded rods, lock washers & nuts

    QTY 1 -

    12" long 1/4" threaded rod
    QTY 4 - 6" long 3/16" threaded rods
    QTY 2 - 1/4" nuts
    QTY 2 - 1/4" lock washers
    QTY 14 - 3/8" nuts
    QTY 8 - 3/8" lock washer

  7. Table Salt
  8. Black Spray Paint (optional)
    Before assembly, you may wish to paint your metal plate black, this creates more visual contrast between the metal & salt.

Step 2: Assemble the Support Base

The concept behind this version of the Chladni plate is to vibrate the metal plate by having direct contact with the speaker. The center rod is connected to the plate with nuts, and is simply allowed to rest on the speaker. To keep the rod from sliding, I just taped it in place. You may opt for glue depending on your speaker. I think I was lucky that on my speaker the cone is a hard piece of plastic. You may need to use a different method of attaching this center rod.

But basically all the weight of the rod itself and plate rests on the center of the speaker. We need a way to keep that plate centered and balanced - that is why we built a middle plate out of acrylic, to hold the rod steady and level.

For the center rod, I used a 1/4" threaded rod. For the support rods, I used 3/8". For the support rods, be sure to get something that'll fit through the speaker's mounting holes - you may need a different size!. Be sure to also pick up 1/4" and 3/8" lock washers & nuts. You can find these rods in lengths of about 4'. Just pick up one of each size and cut them down to the length you need with a hacksaw unless you're lucky enough to find them in the right lengths.

Place a nut on the support rod, put it through the mounting hole and tighten another nut from the bottom. Repeat to create 4 level support rods at equal heights, about 6" above the speaker.

Take your piece of acrylic, mark where the 4 rods touch and drill holes large enough to allow the rods to go through. Also drill a hole in the exact center large enough to allow the center rod to go through. This hole should be just barely large enough to allow the center rod to move freely without binding, but also tight enough to keep it level.

Mount the piece of acrylic to the 4 support rods by screwing a 3/8" nut down the rod. Then place a lock washer, the acrylic sheet, another lock washer, and another nut. Adjust each corner so the sheet is level, then tighten.

Step 3: Assemble the Plate

With your 18" square sheet of metal, drill a hole in the exact center - large enough to just allow the 1/4" center rod to thread into the sheet. An easy trick to marking the center of a square is to take a yardstick/straight edge and draw a line from each opposite corner of the square, forming an X. Where the 2 lines meet is the center.

Now connect your center rod to the plate using the 1/4" nuts & lock washers. Order should be nut, washer, plate, then another washer and nut. This will keep the plate connected tightly and with all the vibrations, the lock washers should prevent anything from coming loose.

On a level surface, place the center rod through the center hole in your acrylic. Make sure the plate is level horizontally by adjusting the where the rod meets the speaker. Once you're satisfied, use a piece of duct tape to secure the rod into place. Later, you may wish to glue/epoxy it into place.

Step 4: Hook Up the Amplifier & Speaker

Rather than use some complicated/expensive tone generator I opted to go the cheapest route possible - free! Using things I had around the house... Basically I used the website here Online Tone Generator to generate tones from my laptop to feed into the speaker. However, because the level coming out of your computer's headphone jack can't power a big 8" subwoofer, you'll have to use an amplifier in-between. You can use a home stereo receiver or in my case - a guitar amplifier. As long as it has a 3.5mm audio jack auxiliary input, you should be good to go! I used the 3.5mm audio cable (sometimes called an mp3 cable) to go from my computer's headphone jack to the amp's aux input. Then detached the amplifier's speaker in the back, and in it's place ran a piece of 12 gauge speaker wire to my subwoofer. Most likely the way you are going to hook this up will be different than me.

Step 5: Fire It Up!

Pour a good amount of salt on top of the plate, distributed evenly. Now may be a good time to mention this can be messy! Get yourself a large box, and cut out the bottom to put this whole rig into - cleanup will be much easier this way.

Start with the volume down low. For a subwoofer, it'll work best if you use very low frequencies. Start at around 100 Hz. You may be able to go lower than that. I got good results in the range between 80 - 250 Hz, YMMV. Slowly increase the volume until the salt starts to vibrate. If you crank it up too high, all the salt will just vibrate right off the plate. Have fun making pretty nodal patterns!

Step 6: Results & Video

Here you'll see the Chladni plate forming patterns at different frequencies. Also are a number of photographs of different patterns that we used for my son's science project.

Explore Science Contest

Third Prize in the
Explore Science Contest