How to Easily Make a Device That Sees Sound

A resonant speaker or vibrating speaker is a type of speaker that produces sound by vibrating a plate attached to it.

When I learned about this, I thought that I could easily make a device to view Chladni figures using it. I made a prototype, and it worked, so I will introduce it here.

There are several projects on Instructables that visualize sound. According to them, the necessary parts are as follows.

1. Plate
2. Speaker
3. Parts to transmit the sound from the speaker to the plate
4. Audio amplifier
5. Power supply for the audio amplifier
6. Tone generator

By using a Bluetooth-enabled vibrating speaker, the number of components can be significantly reduced as follows:

1. Plate: I used an iron plate
2. Speaker: I used a vibrating speaker
3. Component to transmit the speaker's sound to the board: Since the vibrating speaker can be attached to the iron plate using magnets, no special components are required
4. Audio amplifier: Not required since it is included in the vibrating speaker
5. Power supply for the audio amplifier: Not required if using a vibrating speaker with a built-in battery
6. Tone generator: Can be replaced with an app on a smartphone or tablet

Since 3D-printed components are used, a 3D printer is also required.

If using different vibrating speakers, springs, or iron plates than those I used, changes to the component shapes will be necessary. In such cases, open “Chladni Plate Holder.f3d” in Fusion and modify the parameters.

1. Bluetooth-enabled vibrating speaker
2. I used the following items. It came with a magnetic sheet with double-sided tape, so I used that. It also came with suction cups with double-sided tape, but they didn't stick well enough and the speaker fell off due to its own weight, so I didn't use them.
3. https://www.amazon.co.jp/dp/B0DMVWYDXR
4. Iron plate
5. I used a 300 mm x 300 mm x 1 mm plate.
6. https://www.amazon.co.jp/dp/B08KCNS9KV
7. Springs
8. Since I didn't know beforehand what kind of springs would be needed, I purchased a spring set. Four springs are required.
9. https://www.amazon.co.jp/dp/B0CGRCSBZC
10. Double-ring hooks
11. Since I didn't know beforehand what kind of hooks would be needed, I purchased a set. In the end, I used 10mm ones. Four are required.
12. https://www.amazon.co.jp/dp/B0C9Q77VMJ
13. Salt
14. I used salt, but it seems that colored sand is sometimes used as well.
15. A smartphone or tablet device with a tone generator app installed
16. I used the “Audio Function Generator” app on an iPad. Feel free to choose your preferred app.
17. 3D-printed parts for securing the iron plate and collecting spilled salt

Print the following parts with a 3D printer in the specified quantities. No supports are required for any of these parts.

1. holder: 4 pieces
2. connector: 4 pieces
3. connector bolt: 16 pieces
4. foot: 4 pieces
5. sp_center: 1 piece
6. sp_holder: 4 pieces

The following are optional, so print them as needed. These are used to flatten salt that has piled up unevenly.

1. rake: 1 piece
2. rake 2: 1 piece

Align the holes in the holders and connectors, and secure them with connector bolts. Connect the four holders to create a frame like the one in the last photo. If the bolts are screwed in properly, the connector surface should be flat.

Use a drill to drill holes in the four corners of the iron plate. I drilled the holes about 5 mm from the edge.

As shown in the first photo, pass the double round rings through the holes opened at the four corners. Then, as shown in the second photo, attach the spring there.

The spring used was the shortest one in the spring set. When measured, it had a diameter of 5 mm, a spring length of 10 mm, a total length of 18 mm, and a wire thickness of approximately 0.5 mm.

If using a different spring, you may need to modify the shape of the hook attached to the foot. Open the attached “Chladni Plate Holder.f3d” file and adjust the parameters. The relevant parameters are hook_width, hook_distance, and hook_height.

Place the iron plate as shown in the first photo. Next, insert the hook part of the foot into the long hole in the corner of the frame as shown in the second photo, and hook it onto the spring ring. Pull the spring outwards and insert the foot into the holder as shown in the third photo. Repeat this four times to lift the iron plate.

Look from below; if the iron plate is floating as shown in the fourth photo, the process is successful. If the iron plate is in contact with the holder, you will need to replace the spring with a shorter one or modify the shape of the hook on the foot as described in the previous step.

Turn the whole thing upside down and attach the vibrating speaker to the center. Attach a magnetic sheet to the speaker in advance.

Initially, I tested the sound in this state, but encountered an issue where the speaker moved due to vibrations. To address this, I added positioning components: sp_center and sp_holder. Insert the cylinder of sp_center into sp_holder, then insert the opposite side of sp_holder into the foot, resulting in the configuration shown in the third photo.

sp_center must be modeled to match the size of the vibrating speaker. The relevant parameter is speaker_diameter.

All you have to do is sprinkle salt on the iron plate and play sound from the speaker, but it is a good idea to check that the iron plate is level.

If the salt grains move in one direction, the iron plate may be tilted. I adjusted the iron plate to make it level by placing folded paper under the feet.

Since the sound will be loud, it is a good idea to let the people around you know before conducting the experiment.

When collecting the salt after the experiment, you can use the holes at the four corners. Drop the salt into these holes, then remove the foot, which will function as a container.

Attached are the results of 100 experiments conducted at 100Hz intervals from 100Hz to 10kHz.

I was surprised to find that there were quite a few frequencies at which the salt grains hardly moved at all. Additionally, as the frequency increased, the movement of the salt grains slowed down, and it took longer for patterns to form. I felt there was a lack of power, but since I couldn't play the sound too loudly at home, it might be better to consider using smaller salt grains or thinner iron plates.

The photos had red and yellow colors mixed in, so using these colors for 3D printing was a mistake. I think using black filament would have been better.

Considering that the movement of the salt grains might be affected by the speaker floating, I tried making a stand to support the speaker, but the result remained unchanged.