Chladni Patterns on a Square Plate

Have you considered real time, stroboscopic holographic interferometry? I performed it both with a round plate and with a violin... You will get not only visual amplitude information but also visual phase information...

yes - used holographic interferometry quite a bit while in grad school to look at guitars, snare drums, wine glasses, etc. More recently, we've used it to explore the vibration of golf club heads, car doors, automobile transmissions, as well as more musical instruments.

I am not referring to time average interferometry or double exposure interferometry but real time, stroboscopic, holographic interferometry? The fringes slowly move if the strobe frequency is a hertz or two different from the vibration frequency

Yup - we've done that also. But, unfortunately don't have any recent video. I think I have some older video of real time stroboscopic holographic interferometry of a standing sound wave in a rectangular waveguide. I'll have to see if I can convert it from vhs to digital and post it.

Does anyone have any java code on creating chladni patterns,particularly to work through processing open source

Cheers

I wish someone would make this in 3d using two liquids of similar density.
There patterns we see are fascinating but one gets a sense that we are only seeing a part of the structure.

The cross-section is good, though, because there are no layers blocking the view. What kinds of liquids could you use?

I get that that a 2d view has a great value, it seems odd though that materials such as ferro fluid, nano particles, and other exotic substances aren't being examined under the influence of sound. Magnetic fields could also perhaps be employed. There must me a host of transparent mineral oils with requisite properties, various dyes and inks could be added as required..
or interactions of phonons.

and what did u learn?

nodes and antinodes