Physics and music education - Chladni plates

[fiddlerdan]

Chladni plate constructionChladni plates refer to a vibrating plate onto which fine particles like tea, sand or salt are placed. The plate is then vibrated by a speaker directly coupled to the plate. Depending on the frequency of the sound and the shape of the plate  geometric patterns are formed. The particles come to rest in sound waves nodes to make these patterns. The patterns are from standing waves created in the plates based on the excitation and reflections of sound. 

Old school Chladni plates were often excited by running a violin bow along the edge of them, but with a speaker you can deliver precise frequency of sound and at much higher amplitudes. Luthiers use these to tune the plates of violins to get them sounding just right.

The examples below are for my wife's STEM science trip on the Maths of music and motion to the Northern Territory communities. The setup has been made to be portable so its a smallish speaker (I used a car speaker), an ebay audio amplifier module,  some gluing of a 50mm PVC conduit onto the speaker it to make a housing for the plates to be mounted. Its battery powered (courtesy of an Ozito power drill) and reversing the charger mounting clip.

Symmetry of 440Hz (concert pitch A) on a circular Chladni plate 440Hz on a violin shaped plate

With a circular plate you get nice annular symmetry of the patterns,  and one of a violin to show some of the complexity there.

For this trip as my wife Charlie is also talking about hearing I have also made a liner model to represent the cochlear (if it was unrolled) and kids are asked to imagine them as the little hairs in their ears. Education about the ear is particularly important outback as almost half of indigenous children have hearing loss owing to a particular infection that spreads in their communities. So a bit of fun really engages the learning aspects of it as well.

Just for fun we are not only putting pure tones through the plates using an audio generator (a computer or smart phone APP) , but also Beethovens 5th and direct feed in from an electric violin to add to the fun for musicians. I'd include some videos of all the salt particles jumping around if i could...its really engaging from an educational point of view.

Teaching for a resonant frequency using an electric violin as an input sourceResonance on the Chladni plate using a violin as a source (violins generate many complex harmonics)

[EricL]

Hello @fiddlerdan

Thank you very much for posting that very interesting physics demonstration. It's an excellent demonstration of resonance and how we can physically see the form it takes with the help of tea, sand, or salt. But I'm even more impressed with how you put the assembly together. Is the output of the violin directly connected to the speaker or does it pass through the little amp you purchased?

Again, thank you so much for sharing this amazing resonance assembly project.

Eric

[fiddlerdan]

The output from the violin (which has a built in pre-amp) goes through the amp module (see below ~$10 on ebay ). The 18v supply from the Ozitobattery gives you +/- 9v so you can get decent volume.

 I borrowed it from my gig box

Bunnings really is the perfect goto place for STEM education, so much of STEM literacy is about tinkering and putting things together to work (Thats with my professional hat on asa university researcher designing educational experiences for primary kids - where they make choices about wether STEM (science , technology, engineering and maths)  is interesting and build their foundational skills for the future. 

[EricL]

Hi @fiddlerdan

Thank you very much for that extra information about the violin set-up. I'm sure seeing the actual projects for themselves and knowing that they can assemble something similar means that you've successfully inspired them. Once inspired they will possibly seek to know more about STEM.

Eric