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PROJECTS: Chladni PlaTE makezine.com/16/chladni

Make: Volume 16

Vibrating surfaces move and flex in some places while remaining relatively still in others. Powder sprinkled on a flat, vibrating surface will flee the moving areas and settle in the still areas. When the vibrations are steady and at the right frequency, this creates a pattern of standing waves that shows how the material is vibrating.

PATTERNSThe pattern depends on the shape of the surface and the frequency of the vibrations; higher frequencies produce denser patterns. Since acoustic musical instruments produce sound by vibrating, these visualizations can be used to understand and improve an instrument’s design.

WaVE WaTCh

hOW iT WORKSA speaker’s magnet assembly has a ring magnet, a pole piece, and front and rear plates that hold them together.

The ring magnet creates the magnetic field that the voice coil pushes against.

The pole piece helps contain and shape the magnetic field.

The voice coil consists of a thin-walled former and the coil itself, the wire wound around it. Electricity moving back and forth through the wire turns the coil into an electromagnet of varying polarity and strength that moves within the ring magnet’s field.

The voice coil connects to the plate.

The signal generator feeds a pure oscillating signal into the voice coil, and the resulting vibra-tions travel outward and bounce back from the plate edges. We adjust the signal’s frequency, and when the plate can physically resonate at a particular frequency, it settles into a stable pattern: a standing wave.

The nodes are the still areas where the powder collects. The antinodes are the clean areas where the plate moves the most.

1 Ring magnet

2 Front plate

3 Rear plate

4 Pole piece

5 Voice coil

6 Former

7 Spider

8 Vent

9 Signal wires

1 1

2 2

4 4

5 66 5

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83 3

SPEAKER DRIVER

CHLADNI PLATE AND SHAKER ASSEMBLY

Plastic cup

Screw mount

Plate

Aluminum tape

Voice coil

Ring magnet

9