A lot of people use a piezo but I found this to be to small to produce a good effect. I ran across a website Cymatics which had a link to a wave driver you could buy and after looking it over I realized it was just a modified speaker which could be easily made for cheap. This is my first instructable.
Step 1: Materials and Tools and Misc
A discarded 8" speaker with its coil intact
small sink strainer
cardboard (an old cereal box)
heavy canvas (optional)
8-32 X 6" threaded rod (1)
3/8 X .171 X 1 Nylon spacer (1)
8-32 Insert Lock Nuts (4)
Metals spacers (4)
8-32 screws (8)
9 1/2" X 9 1/2" metal plate (cut from old VCR casing)
Sabre Saw with Sheet Metal Blade
This project involves cutting metal and plexiglass with a sabre saw, which can be dangerous.
Plexiglass is not easy to work with at this thickness. It cracks, shatters, and melts. You might want to use wood or metal instead of plexiglass.
Step 2: The Old Speaker
Measure the bottom inside of the speaker. Use this measurement to cut a circle of cardboard out the same diameter as the lip running around bottom inside of speaker. Center the coil form on the circle of cardboard and trace around with pencil. Then use a razor blade to cut out inside circle. I also cut out a circle of canvas to sit on top of cardboard. which is really not needed but looks better. You should have a cardboard doughnut now.
There should be a lip with some paper still attached around the coil form. Insert the coil into the canvas and the cardboard and then push them flush against the lip of the coil form. Hot glue into place. Then set the coil form with attached cardboard back into slot. Check to make sure coil does not bind in slot, it should move with a bit of pressure. The cardboard sits on lip of speaker frame. Hot glue outside of circle onto frame.
Step 3: Support Frame and Plexiglass
Flip the speaker over face down on the plexiglass and trace around with marker. My speaker had mounting holes around the outer edge so I used those to mark out the center of the circle. Just mark holes then use a ruler to draw X through circle connecting the hole marks.
A sabre saw with a metal cutting blade cuts plexiglass easy enough the only problem is melt-back. As soon as you cut past a place it melts back together! So cut around your circle leaving a groove of melted plexi. Then fill this groove with metal cutting oil and go back around very slowly adding oil when necessary. (If anyone has found an easier way please tell me!)
Drill a 3/8" hole in exact center of plexiglass disc. I used a bolt to chuck the disc in a drill and then clamped the drill using it as mini lathe to grind/sand down the plexi edges smooth.
Step 4: Vibrating Rod
Now place strainer on top of coil form in speaker. Make sure the metal is not shorting speaker wires. Use hot glue to level out and then hot glue into place.
Step 5: Mounting Plexiglass, Testing
Now would be a good time to test on a Function Generator with an amplifier. I use an old 30W amp but will probably make a smaller one for the science fair.
The rod should vibrate freely in the guide.
Step 6: Chladni Plate
Most people use salt or sand to create the different figures. I have found that frequencies between 800 to 2000 hz work really well. Go slow on the dial to find the sweet spots and you will have to play with amplitude a bit to, but its not that hard.
This picture is just below 1000 hz.